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);
```

1 files changed, 2 insertions, 2 deletions

diff --git a/src/model/guild/emoji.rs b/src/model/guild/emoji.rs
index 4a2190f..7f332ae 100644
--- a/src/model/guild/emoji.rs
+++ b/src/model/guild/emoji.rs
@@ -151,8 +151,8 @@ impl Emoji {
     /// ```
     #[cfg(feature = "cache")]
     pub fn find_guild_id(&self) -> Option<GuildId> {
-        for guild in CACHE.read().unwrap().guilds.values() {
-            let guild = guild.read().unwrap();
+        for guild in CACHE.read().guilds.values() {
+            let guild = guild.read();
 
             if guild.emojis.contains_key(&self.id) {
                 return Some(guild.id);