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, 1 deletions

diff --git a/src/client/context.rs b/src/client/context.rs
index 2288f28..18500d6 100644
--- a/src/client/context.rs
+++ b/src/client/context.rs
@@ -83,7 +83,7 @@ impl Context {
 
         feature_cache! {
             {
-                let cache = CACHE.read().unwrap();
+                let cache = CACHE.read();
 
                 map.insert("username".to_string(), Value::String(cache.user.name.clone()));