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/framework/standard/mod.rs b/src/framework/standard/mod.rs
index a44c6e7..c3f0d70 100644
--- a/src/framework/standard/mod.rs
+++ b/src/framework/standard/mod.rs
@@ -400,7 +400,7 @@ impl StandardFramework {
 
     #[cfg(feature = "cache")]
     fn is_blocked_guild(&self, message: &Message) -> bool {
-        if let Some(Channel::Guild(channel)) = CACHE.read().unwrap().channel(message.channel_id) {
+        if let Some(Channel::Guild(channel)) = CACHE.read().channel(message.channel_id) {
             let guild_id = channel.with(|g| g.guild_id);
             if self.configuration.blocked_guilds.contains(&guild_id) {
                 return true;
@@ -510,7 +510,8 @@ impl StandardFramework {
             } else {
                 if !command.allowed_roles.is_empty() {
                     if let Some(guild) = message.guild() {
-                        let guild = guild.read().unwrap();
+                        let guild = guild.read();
+
                         if let Some(member) = guild.members.get(&message.author.id) {
                             if let Ok(permissions) = member.permissions() {
                                 if !permissions.administrator() {