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, 4 insertions, 4 deletions

diff --git a/src/model/guild/role.rs b/src/model/guild/role.rs
index 7ac7019..3ed718e 100644
--- a/src/model/guild/role.rs
+++ b/src/model/guild/role.rs
@@ -106,8 +106,8 @@ impl Role {
     /// [`ModelError::GuildNotFound`]: enum.ModelError.html#variant.GuildNotFound
     #[cfg(feature = "cache")]
     pub fn find_guild(&self) -> Result<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.roles.contains_key(&RoleId(self.id.0)) {
                 return Ok(guild.id);
@@ -168,10 +168,10 @@ impl RoleId {
     /// Search the cache for the role.
     #[cfg(feature = "cache")]
     pub fn find(&self) -> Option<Role> {
-        let cache = CACHE.read().unwrap();
+        let cache = CACHE.read();
 
         for guild in cache.guilds.values() {
-            let guild = guild.read().unwrap();
+            let guild = guild.read();
 
             if !guild.roles.contains_key(self) {
                 continue;