Switch to parking_lot::{Mutex, RwLock}

Switch to the `parking_lot` crate's implementations of
`std::sync::Mutex` and `std::sync::RwLock`, which are more efficient.

A writeup on why `parking_lot` is more efficient can be read here:
<https://github.com/Amanieu/parking_lot>

Upgrade path:

Modify `mutex.lock().unwrap()` usage to `mutex.lock()` (not needing to
unwrap or handle a result), and
`rwlock.read().unwrap()`/`rwlock.write().unwrap()` usage to
`rwlock.read()` and `rwlock.write()`.

For example, modify:

```rust
use serenity::CACHE;

println!("{}", CACHE.read().unwrap().user.id);
```

to:

```rust
use serenity::CACHE;

println!("{}", CACHE.read().user.id);
```

2 files changed, 15 insertions, 15 deletions

diff --git a/src/builder/create_embed.rs b/src/builder/create_embed.rs
index a6b264c..f7dc0b1 100644
--- a/src/builder/create_embed.rs
+++ b/src/builder/create_embed.rs
@@ -249,20 +249,20 @@ impl CreateEmbed {
     /// impl EventHandler for Handler {
     ///     fn on_guild_member_addition(&self, _: Context, guild_id: GuildId, member: Member) {
     ///         use serenity::client::CACHE;
-    ///         let cache = CACHE.read().unwrap();
+    ///         let cache = CACHE.read();
     ///
     ///         if let Some(guild) = cache.guild(guild_id) {
-    ///             let guild = guild.read().unwrap();
+    ///             let guild = guild.read();
     ///
     ///             let channel_search = guild
     ///                 .channels
     ///                 .values()
-    ///                 .find(|c| c.read().unwrap().name == "join-log");
+    ///                 .find(|c| c.read().name == "join-log");
     ///
     ///             if let Some(channel) = channel_search {
-    ///                 let user = member.user.read().unwrap();
+    ///                 let user = member.user.read();
     ///
-    ///                 let _ = channel.read().unwrap().send_message(|m| m
+    ///                 let _ = channel.read().send_message(|m| m
     ///                     .embed(|e| {
     ///                         let mut e = e
     ///                             .author(|a| a.icon_url(&user.face()).name(&user.name))
diff --git a/src/builder/create_invite.rs b/src/builder/create_invite.rs
index 5f4f0bf..d719c17 100644
--- a/src/builder/create_invite.rs
+++ b/src/builder/create_invite.rs
@@ -21,7 +21,7 @@ use internal::prelude::*;
 ///     fn on_message(&self, _: Context, msg: Message) {
 ///         use serenity::client::CACHE;
 ///         if msg.content == "!createinvite" {
-///             let channel = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
+///             let channel = match CACHE.read().guild_channel(msg.channel_id) {
 ///                 Some(channel) => channel,
 ///                 None => {
 ///                     let _ = msg.channel_id.say("Error creating invite");
@@ -30,7 +30,7 @@ use internal::prelude::*;
 ///                 },
 ///             };
 ///
-///             let reader = channel.read().unwrap();
+///             let reader = channel.read();
 ///
 ///             let invite = match reader.create_invite(|i| i.max_age(3600).max_uses(10)) {
 ///                 Ok(invite) => invite,
@@ -77,8 +77,8 @@ impl CreateInvite {
     /// # use std::error::Error;
     /// #
     /// # fn try_main() -> Result<(), Box<Error>> {
-    /// #     let channel = CACHE.read().unwrap().guild_channel(81384788765712384).unwrap();
-    /// #     let channel = channel.read().unwrap();
+    /// #     let channel = CACHE.read().guild_channel(81384788765712384).unwrap();
+    /// #     let channel = channel.read();
     /// #
     /// let invite = channel.create_invite(|i| i.max_age(3600))?;
     /// #     Ok(())
@@ -111,8 +111,8 @@ impl CreateInvite {
     /// # use std::error::Error;
     /// #
     /// # fn try_main() -> Result<(), Box<Error>> {
-    /// #     let channel = CACHE.read().unwrap().guild_channel(81384788765712384).unwrap();
-    /// #     let channel = channel.read().unwrap();
+    /// #     let channel = CACHE.read().guild_channel(81384788765712384).unwrap();
+    /// #     let channel = channel.read();
     /// #
     /// let invite = channel.create_invite(|i| i.max_uses(5))?;
     /// #     Ok(())
@@ -143,8 +143,8 @@ impl CreateInvite {
     /// # use std::error::Error;
     /// #
     /// # fn try_main() -> Result<(), Box<Error>> {
-    /// #     let channel = CACHE.read().unwrap().guild_channel(81384788765712384).unwrap();
-    /// #     let channel = channel.read().unwrap();
+    /// #     let channel = CACHE.read().guild_channel(81384788765712384).unwrap();
+    /// #     let channel = channel.read();
     /// #
     /// let invite = channel.create_invite(|i| i.temporary(true))?;
     /// #     Ok(())
@@ -175,8 +175,8 @@ impl CreateInvite {
     /// # use std::error::Error;
     /// #
     /// # fn try_main() -> Result<(), Box<Error>> {
-    /// #     let channel = CACHE.read().unwrap().guild_channel(81384788765712384).unwrap();
-    /// #     let channel = channel.read().unwrap();
+    /// #     let channel = CACHE.read().guild_channel(81384788765712384).unwrap();
+    /// #     let channel = channel.read();
     /// #
     /// let invite = channel.create_invite(|i| i.unique(true))?;
     /// #     Ok(())