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, 13 insertions, 0 deletions

diff --git a/src/internal/rwlock_ext.rs b/src/internal/rwlock_ext.rs
index 8266cdf..6235370 100644
--- a/src/internal/rwlock_ext.rs
+++ b/src/internal/rwlock_ext.rs
@@ -1,3 +1,4 @@
+use parking_lot::RwLock as ParkingLotRwLock;
 use std::sync::{Arc, RwLock};
 
 pub trait RwLockExt<T> {
@@ -16,3 +17,15 @@ impl<T> RwLockExt<T> for Arc<RwLock<T>> {
         f(&mut w)
     }
 }
+
+impl<T> RwLockExt<T> for Arc<ParkingLotRwLock<T>> {
+    fn with<Y, F: Fn(&T) -> Y>(&self, f: F) -> Y {
+        let r = self.read();
+        f(&r)
+    }
+
+    fn with_mut<Y, F: FnMut(&mut T) -> Y>(&self, mut f: F) -> Y {
+        let mut w = self.write();
+        f(&mut w)
+    }
+}