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/utils/mod.rs b/src/utils/mod.rs
index 4b36b73..c6d27c3 100644
--- a/src/utils/mod.rs
+++ b/src/utils/mod.rs
@@ -455,7 +455,7 @@ pub fn shard_id(guild_id: u64, shard_count: u64) -> u64 { (guild_id >> 22) % sha
 #[cfg(feature = "cache")]
 pub fn with_cache<T, F>(f: F) -> T
     where F: Fn(&Cache) -> T {
-    let cache = CACHE.read().unwrap();
+    let cache = CACHE.read();
     f(&cache)
 }
 
@@ -476,6 +476,6 @@ pub fn with_cache<T, F>(f: F) -> T
 #[cfg(feature = "cache")]
 pub fn with_cache_mut<T, F>(mut f: F) -> T
     where F: FnMut(&mut Cache) -> T {
-    let mut cache = CACHE.write().unwrap();
+    let mut cache = CACHE.write();
     f(&mut cache)
 }