Monomorphize all functions

This commit monomorphizes all functions, turning functions like:

```rust
fn foo<T: Into<Bar>>(baz: T) {
    baz = baz.into();

    // function here
}
```

Into functions like:

```rust
fn foo<T: Into<Bar>>(baz: T) {
    _foo(baz.into())
}

fn _foo(baz: Bar) {
    // function here
}
```

This avoids binary bloat and improves build times, by reducing the amount of
code duplication.

7 files changed, 144 insertions, 47 deletions

diff --git a/src/builder/create_embed.rs b/src/builder/create_embed.rs
index c3c4cb0..48ea19d 100644
--- a/src/builder/create_embed.rs
+++ b/src/builder/create_embed.rs
@@ -65,14 +65,20 @@ impl CreateEmbed {
     /// [`colour`]: #method.colour
     #[cfg(feature = "utils")]
     #[inline]
-    pub fn color<C: Into<Colour>>(self, colour: C) -> Self { self.colour(colour.into()) }
+    pub fn color<C: Into<Colour>>(self, colour: C) -> Self { self.colour(colour) }
 
     /// Set the colour of the left-hand side of the embed.
     #[cfg(feature = "utils")]
-    pub fn colour<C: Into<Colour>>(mut self, colour: C) -> Self {
+    #[inline]
+    pub fn colour<C: Into<Colour>>(self, colour: C) -> Self {
+        self._colour(colour.into())
+    }
+
+    #[cfg(feature = "utils")]
+    fn _colour(mut self, colour: Colour) -> Self {
         self.0.insert(
             "color",
-            Value::Number(Number::from(u64::from(colour.into().0))),
+            Value::Number(Number::from(u64::from(colour.0))),
         );
 
         self
@@ -99,10 +105,15 @@ impl CreateEmbed {
     /// Set the description of the embed.
     ///
     /// **Note**: This can't be longer than 2048 characters.
-    pub fn description<D: Display>(mut self, description: D) -> Self {
+    #[inline]
+    pub fn description<D: Display>(self, description: D) -> Self {
+        self._description(description.to_string())
+    }
+
+    fn _description(mut self, description: String) -> Self {
         self.0.insert(
             "description",
-            Value::String(description.to_string()),
+            Value::String(description),
         );
 
         self
@@ -113,8 +124,13 @@ impl CreateEmbed {
     ///
     /// **Note**: Maximum amount of characters you can put is 256 in a field
     /// name and 1024 in a field value.
-    pub fn field<T, U>(mut self, name: T, value: U, inline: bool) -> Self
+    #[inline]
+    pub fn field<T, U>(self, name: T, value: U, inline: bool) -> Self
         where T: Display, U: Display {
+        self._field(name.to_string(), value.to_string(), inline)
+    }
+
+    fn _field(mut self, name: String, value: String, inline: bool) -> Self {
         {
             let entry = self.0
                 .entry("fields")
@@ -123,8 +139,8 @@ impl CreateEmbed {
             if let Value::Array(ref mut inner) = *entry {
                 inner.push(json!({
                     "inline": inline,
-                    "name": name.to_string(),
-                    "value": value.to_string(),
+                    "name": name,
+                    "value": value,
                 }));
             }
         }
@@ -177,13 +193,21 @@ impl CreateEmbed {
     /// Set the image associated with the embed. This only supports HTTP(S).
     #[inline]
     pub fn image<S: AsRef<str>>(self, url: S) -> Self {
-        self.url_object("image", url.as_ref())
+        self._image(url.as_ref())
+    }
+
+    fn _image(self, url: &str) -> Self {
+        self.url_object("image", url)
     }
 
     /// Set the thumbnail of the embed. This only supports HTTP(S).
     #[inline]
     pub fn thumbnail<S: AsRef<str>>(self, url: S) -> Self {
-        self.url_object("thumbnail", url.as_ref())
+        self._thumbnail(url.as_ref())
+    }
+
+    fn _thumbnail(self, url: &str) -> Self {
+        self.url_object("thumbnail", url)
     }
 
     /// Set the timestamp.
@@ -272,25 +296,37 @@ impl CreateEmbed {
     ///
     /// client.start().unwrap();
     /// ```
-    pub fn timestamp<T: Into<Timestamp>>(mut self, timestamp: T) -> Self {
-        self.0
-            .insert("timestamp", Value::String(timestamp.into().ts));
+    #[inline]
+    pub fn timestamp<T: Into<Timestamp>>(self, timestamp: T) -> Self {
+        self._timestamp(timestamp.into())
+    }
+
+    fn _timestamp(mut self, timestamp: Timestamp) -> Self {
+        self.0.insert("timestamp", Value::String(timestamp.ts));
 
         self
     }
 
     /// Set the title of the embed.
-    pub fn title<D: Display>(mut self, title: D) -> Self {
-        self.0
-            .insert("title", Value::String(title.to_string()));
+    #[inline]
+    pub fn title<D: Display>(self, title: D) -> Self {
+        self._title(title.to_string())
+    }
+
+    fn _title(mut self, title: String) -> Self {
+        self.0.insert("title", Value::String(title));
 
         self
     }
 
     /// Set the URL to direct to when clicking on the title.
-    pub fn url<S: AsRef<str>>(mut self, url: S) -> Self {
-        self.0
-            .insert("url", Value::String(url.as_ref().to_string()));
+    #[inline]
+    pub fn url<S: AsRef<str>>(self, url: S) -> Self {
+        self._url(url.as_ref())
+    }
+
+    fn _url(mut self, url: &str) -> Self {
+        self.0.insert("url", Value::String(url.to_string()));
 
         self
     }
@@ -301,8 +337,13 @@ impl CreateEmbed {
     /// with the provided filename. Or else this won't work.
     ///
     /// [`ChannelId::send_files`]: ../model/id/struct.ChannelId.html#send_files
+    #[inline]
     pub fn attachment<S: AsRef<str>>(self, filename: S) -> Self {
-        self.image(&format!("attachment://{}", filename.as_ref()))
+        self._attachment(filename.as_ref())
+    }
+
+    fn _attachment(self, filename: &str) -> Self {
+        self.image(&format!("attachment://{}", filename))
     }
 }
 
diff --git a/src/builder/create_message.rs b/src/builder/create_message.rs
index df6f4d5..a5ede5a 100644
--- a/src/builder/create_message.rs
+++ b/src/builder/create_message.rs
@@ -46,8 +46,13 @@ impl CreateMessage {
     /// Set the content of the message.
     ///
     /// **Note**: Message contents must be under 2000 unicode code points.
-    pub fn content<D: Display>(mut self, content: D) -> Self {
-        self.0.insert("content", Value::String(content.to_string()));
+    #[inline]
+    pub fn content<D: Display>(self, content: D) -> Self {
+        self._content(content.to_string())
+    }
+
+    fn _content(mut self, content: String) -> Self {
+        self.0.insert("content", Value::String(content));
 
         self
     }
@@ -75,8 +80,13 @@ impl CreateMessage {
     }
 
     /// Adds a list of reactions to create after the message's sent.
-    pub fn reactions<R: Into<ReactionType>, It: IntoIterator<Item=R>>(mut self, reactions: It) -> Self {
-        self.1 = Some(reactions.into_iter().map(|r| r.into()).collect());
+    #[inline]
+    pub fn reactions<R: Into<ReactionType>, It: IntoIterator<Item=R>>(self, reactions: It) -> Self {
+        self._reactions(reactions.into_iter().map(Into::into).collect())
+    }
+
+    fn _reactions(mut self, reactions: Vec<ReactionType>) -> Self {
+        self.1 = Some(reactions);
 
         self
     }
diff --git a/src/builder/edit_channel.rs b/src/builder/edit_channel.rs
index b8d897b..e1b62a7 100644
--- a/src/builder/edit_channel.rs
+++ b/src/builder/edit_channel.rs
@@ -80,13 +80,16 @@ impl EditChannel {
     ///
     /// [text]: ../model/channel/enum.ChannelType.html#variant.Text
     /// [voice]: ../model/channel/enum.ChannelType.html#variant.Voice
-    pub fn category<C>(mut self, category: C) -> Self
-        where C: Into<Option<ChannelId>> {
-        let parent_id = match category.into() {
+    #[inline]
+    pub fn category<C: Into<Option<ChannelId>>>(self, category: C) -> Self {
+        self._category(category.into())
+    }
+
+    fn _category(mut self, category: Option<ChannelId>) -> Self {
+        self.0.insert("parent_id", match category {
             Some(c) => Value::Number(Number::from(c.0)),
             None => Value::Null
-        };
-        self.0.insert("parent_id", parent_id);
+        });
 
         self
     }
diff --git a/src/builder/edit_guild.rs b/src/builder/edit_guild.rs
index c24b9b4..28abda7 100644
--- a/src/builder/edit_guild.rs
+++ b/src/builder/edit_guild.rs
@@ -23,11 +23,16 @@ impl EditGuild {
     /// valid.
     ///
     /// [`afk_timeout`]: #method.afk_timeout
-    pub fn afk_channel<C: Into<ChannelId>>(mut self, channel: Option<C>) -> Self {
+    #[inline]
+    pub fn afk_channel<C: Into<ChannelId>>(self, channel: Option<C>) -> Self {
+        self._afk_channel(channel.map(Into::into))
+    }
+
+    fn _afk_channel(mut self, channel: Option<ChannelId>) -> Self {
         self.0.insert(
             "afk_channel_id",
             match channel {
-                Some(channel) => Value::Number(Number::from(channel.into().0)),
+                Some(channel) => Value::Number(Number::from(channel.0)),
                 None => Value::Null,
             },
         );
@@ -98,8 +103,13 @@ impl EditGuild {
     /// Transfers the ownership of the guild to another user by Id.
     ///
     /// **Note**: The current user must be the owner of the guild.
-    pub fn owner<U: Into<UserId>>(mut self, user_id: U) -> Self {
-        let id = Value::Number(Number::from(user_id.into().0));
+    #[inline]
+    pub fn owner<U: Into<UserId>>(self, user_id: U) -> Self {
+        self._owner(user_id.into())
+    }
+
+    fn _owner(mut self, user_id: UserId) -> Self {
+        let id = Value::Number(Number::from(user_id.0));
         self.0.insert("owner_id", id);
 
         self
@@ -180,10 +190,14 @@ impl EditGuild {
     ///
     /// [`VerificationLevel`]: ../model/guild/enum.VerificationLevel.html
     /// [`VerificationLevel::High`]: ../model/guild/enum.VerificationLevel.html#variant.High
-    pub fn verification_level<V>(mut self, verification_level: V) -> Self
+    #[inline]
+    pub fn verification_level<V>(self, verification_level: V) -> Self
         where V: Into<VerificationLevel> {
-        let num = Value::Number(Number::from(verification_level.into().num()));
+        self._verification_level(verification_level.into())
+    }
 
+    fn _verification_level(mut self, verification_level: VerificationLevel) -> Self {
+        let num = Value::Number(Number::from(verification_level.num()));
         self.0.insert("verification_level", num);
 
         self
diff --git a/src/builder/edit_member.rs b/src/builder/edit_member.rs
index 19edb5e..c0791d6 100644
--- a/src/builder/edit_member.rs
+++ b/src/builder/edit_member.rs
@@ -50,13 +50,17 @@ impl EditMember {
     /// Requires the [Manage Roles] permission to modify.
     ///
     /// [Manage Roles]: ../model/permissions/constant.MANAGE_ROLES.html
-    pub fn roles<T: AsRef<RoleId>, It: IntoIterator<Item=T>>(mut self, roles: It) -> Self {
-        let role_ids = roles
+    pub fn roles<T: AsRef<RoleId>, It: IntoIterator<Item=T>>(self, roles: It) -> Self {
+        let roles = roles
             .into_iter()
             .map(|x| Value::Number(Number::from(x.as_ref().0)))
             .collect();
 
-        self.0.insert("roles", Value::Array(role_ids));
+        self._roles(roles)
+    }
+
+    fn _roles(mut self, roles: Vec<Value>) -> Self {
+        self.0.insert("roles", Value::Array(roles));
 
         self
     }
@@ -66,8 +70,13 @@ impl EditMember {
     /// Requires the [Move Members] permission.
     ///
     /// [Move Members]: ../model/permissions/constant.MOVE_MEMBERS.html
-    pub fn voice_channel<C: Into<ChannelId>>(mut self, channel_id: C) -> Self {
-        let num = Value::Number(Number::from(channel_id.into().0));
+    #[inline]
+    pub fn voice_channel<C: Into<ChannelId>>(self, channel_id: C) -> Self {
+        self._voice_channel(channel_id.into())
+    }
+
+    fn _voice_channel(mut self, channel_id: ChannelId) -> Self {
+        let num = Value::Number(Number::from(channel_id.0));
         self.0.insert("channel_id", num);
 
         self
diff --git a/src/builder/edit_message.rs b/src/builder/edit_message.rs
index 29da46a..c62f072 100644
--- a/src/builder/edit_message.rs
+++ b/src/builder/edit_message.rs
@@ -26,7 +26,12 @@ impl EditMessage {
     /// Set the content of the message.
     ///
     /// **Note**: Message contents must be under 2000 unicode code points.
-    pub fn content<D: Display>(mut self, content: D) -> Self {
+    #[inline]
+    pub fn content<D: Display>(self, content: D) -> Self {
+        self._content(content.to_string())
+    }
+
+    fn _content(mut self, content: String) -> Self {
         self.0.insert("content", Value::String(content.to_string()));
 
         self
diff --git a/src/builder/get_messages.rs b/src/builder/get_messages.rs
index f302ff0..2d7ee87 100644
--- a/src/builder/get_messages.rs
+++ b/src/builder/get_messages.rs
@@ -55,24 +55,39 @@ pub struct GetMessages(pub VecMap<&'static str, u64>);
 impl GetMessages {
     /// Indicates to retrieve the messages after a specific message, given by
     /// its Id.
-    pub fn after<M: Into<MessageId>>(mut self, message_id: M) -> Self {
-        self.0.insert("after", message_id.into().0);
+    #[inline]
+    pub fn after<M: Into<MessageId>>(self, message_id: M) -> Self {
+        self._after(message_id.into())
+    }
+
+    fn _after(mut self, message_id: MessageId) -> Self {
+        self.0.insert("after", message_id.0);
 
         self
     }
 
     /// Indicates to retrieve the messages _around_ a specific message in either
     /// direction (before+after) the given message.
-    pub fn around<M: Into<MessageId>>(mut self, message_id: M) -> Self {
-        self.0.insert("around", message_id.into().0);
+    #[inline]
+    pub fn around<M: Into<MessageId>>(self, message_id: M) -> Self {
+        self._around(message_id.into())
+    }
+
+    fn _around(mut self, message_id: MessageId) -> Self {
+        self.0.insert("around", message_id.0);
 
         self
     }
 
     /// Indicates to retrieve the messages before a specific message, given by
     /// its Id.
-    pub fn before<M: Into<MessageId>>(mut self, message_id: M) -> Self {
-        self.0.insert("before", message_id.into().0);
+    #[inline]
+    pub fn before<M: Into<MessageId>>(self, message_id: M) -> Self {
+        self._before(message_id.into())
+    }
+
+    fn _before(mut self, message_id: MessageId) -> Self {
+        self.0.insert("before", message_id.0);
 
         self
     }