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, 1 insertions, 2 deletions

diff --git a/src/client/event_handler.rs b/src/client/event_handler.rs
index 6e3c78e..0c618c2 100644
--- a/src/client/event_handler.rs
+++ b/src/client/event_handler.rs
@@ -1,3 +1,4 @@
+use parking_lot::RwLock;
 use serde_json::Value;
 use std::collections::HashMap;
 use std::sync::Arc;
@@ -5,8 +6,6 @@ use super::context::Context;
 use model::event::*;
 use model::*;
 
-use std::sync::RwLock;
-
 pub trait EventHandler {
     #[cfg(feature = "cache")]
     fn on_cached(&self, _: Context, _: Vec<GuildId>) {}