Update doctests for Context changes

Due to the Context having many methods removed, the doctests were
failing.

Update the doctests to use alternative methods to accomplish the same.

Example:

Before:
```rust
context.say("hi");
```

After:
```rust
message.channel_id.say("hi")
```

5 files changed, 14 insertions, 15 deletions

diff --git a/src/utils/builder/create_invite.rs b/src/utils/builder/create_invite.rs
index 0f16b27..b3592d0 100644
--- a/src/utils/builder/create_invite.rs
+++ b/src/utils/builder/create_invite.rs
@@ -17,9 +17,9 @@ use std::default::Default;
 ///
 /// let mut client = Client::login_bot(&env::var("DISCORD_BOT_TOKEN").unwrap());
 ///
-/// client.on_message(|context, message| {
+/// client.on_message(|_, message| {
 ///     if message.content == "!invite" {
-///         let invite = context.create_invite(message.channel_id, |i| i
+///         let invite = message.channel_id.create_invite(|i| i
 ///             .max_age(3600)
 ///             .max_uses(10));
 ///     }
diff --git a/src/utils/builder/create_message.rs b/src/utils/builder/create_message.rs
index 5386c78..90a1f65 100644
--- a/src/utils/builder/create_message.rs
+++ b/src/utils/builder/create_message.rs
@@ -21,10 +21,9 @@ use super::CreateEmbed;
 /// Sending a message with a content of `"test"` and applying text-to-speech:
 ///
 /// ```rust,ignore
-/// // assuming you are in a context
-/// context.send_message(message.channel_id, |m|
-///     .content("test")
-///     .tts(true));
+/// // assuming a `channel_id` has been bound
+///
+/// channel_id.say(|m| m.content("test").tts(true));
 /// ```
 ///
 /// [`Context::say`]: ../../client/struct.Context.html#method.say
diff --git a/src/utils/builder/edit_profile.rs b/src/utils/builder/edit_profile.rs
index 4d25f00..83f1da2 100644
--- a/src/utils/builder/edit_profile.rs
+++ b/src/utils/builder/edit_profile.rs
@@ -22,7 +22,7 @@ impl EditProfile {
     /// ```rust,ignore
     /// use serenity::utils;
     ///
-    /// // assuming you are in a context
+    /// // assuming a `context` has been bound
     ///
     /// let base64 = utils::read_image("./my_image.jpg")
     ///     .expect("Failed to read image");
diff --git a/src/utils/builder/edit_role.rs b/src/utils/builder/edit_role.rs
index 3410417..e9b86e9 100644
--- a/src/utils/builder/edit_role.rs
+++ b/src/utils/builder/edit_role.rs
@@ -19,8 +19,8 @@ use ::model::{Permissions, Role, permissions};
 /// Create a hoisted, mentionable role named "a test role":
 ///
 /// ```rust,ignore
-/// // assuming you are in a `context` and a `guild_id` has been bound
-/// let role = context.create_role(guild_id, |r| r
+/// // assuming a `channel_id` and `guild_id` has been bound
+/// let role = channel_id.create_role(guild_id, |r| r
 ///     .hoist(true)
 ///     .mentionable(true)
 ///     .name("a test role"));
diff --git a/src/utils/builder/search.rs b/src/utils/builder/search.rs
index 6aaffca..904c580 100644
--- a/src/utils/builder/search.rs
+++ b/src/utils/builder/search.rs
@@ -90,9 +90,9 @@ impl SortingOrder {
 /// ascending order, and limiting to 5 results:
 ///
 /// ```rust,ignore
-/// // assuming you are in a context
+/// // assuming a `channel_id` has been bound
 ///
-/// let res = context.search_channel(message.channel_id, |s| s
+/// let res = channel_id.search(|s| s
 ///     .content("rust")
 ///     .has_embed(false)
 ///     .has_attachment(false)
@@ -124,7 +124,7 @@ impl SortingOrder {
 ///     let query = args.join(" ");
 ///
 ///     if query.is_empty() {
-///         let _ = context.say("You must provide a query");
+///         let _ = message.channel_id.say("You must provide a query");
 ///
 ///         return Ok(());
 ///     }
@@ -138,7 +138,7 @@ impl SortingOrder {
 ///         .map(|c| c.id)
 ///         .collect();
 ///
-///     let search = context.search_guild(guild.id, channel_ids, |s| s
+///     let search = guild.search(guild.id, channel_ids, |s| s
 ///         .content(&query)
 ///         .context_size(0)
 ///         .has_attachment(true)
@@ -152,13 +152,13 @@ impl SortingOrder {
 ///         Err(why) => {
 ///             println!("Error performing search '{}': {:?}", query, why);
 ///
-///             let _ = context.say("Error occurred while searching");
+///             let _ = message.channel_id.say("Error occurred while searching");
 ///
 ///             return Ok(());
 ///         },
 ///     };
 ///
-///     let _ = context.send_message(message.channel_id, |m| m
+///     let _ = message.channel_id.send_message(|m| m
 ///         .content(&format!("Found {} total results", messages.total))
 ///         .embed(|mut e| {
 ///             for (i, messages) in messages.results.iter_mut().enumerate() {