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, 3 insertions, 2 deletions

diff --git a/src/model/mod.rs b/src/model/mod.rs
index 0817094..64987e1 100644
--- a/src/model/mod.rs
+++ b/src/model/mod.rs
@@ -32,11 +32,12 @@ pub use self::voice::*;
 pub use self::webhook::*;
 
 use chrono::NaiveDateTime;
+use parking_lot::RwLock;
 use self::utils::*;
 use serde::de::Visitor;
 use std::collections::HashMap;
 use std::fmt::{Display, Formatter, Result as FmtResult};
-use std::sync::{Arc, RwLock};
+use std::sync::Arc;
 use internal::prelude::*;
 
 #[cfg(feature = "utils")]
@@ -67,7 +68,7 @@ macro_rules! id_u64 {
                     self
                 }
             }
-            
+
             impl From<u64> for $name {
                 fn from(id_as_u64: u64) -> $name {
                     $name(id_as_u64)