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);
```

2 files changed, 15 insertions, 15 deletions

diff --git a/examples/05_command_framework/src/main.rs b/examples/05_command_framework/src/main.rs
index 437c44e..975e216 100644
--- a/examples/05_command_framework/src/main.rs
+++ b/examples/05_command_framework/src/main.rs
@@ -199,7 +199,7 @@ command!(about_role(_ctx, msg, args) {
     if let Some(guild) = msg.guild() {
         // `role_by_name()` allows us to attempt attaining a reference to a role
         // via its name.
-        if let Some(role) = guild.read().unwrap().role_by_name(&potential_role_name) {
+        if let Some(role) = guild.read().role_by_name(&potential_role_name) {
             if let Err(why) = msg.channel_id.say(&format!("Role-ID: {}", role.id)) {
                 println!("Error sending message: {:?}", why);
             }
diff --git a/examples/06_voice/src/main.rs b/examples/06_voice/src/main.rs
index 8de2c3b..4c40bb4 100644
--- a/examples/06_voice/src/main.rs
+++ b/examples/06_voice/src/main.rs
@@ -49,8 +49,8 @@ fn main() {
 }
 
 command!(deafen(ctx, msg) {
-    let guild_id = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
-        Some(channel) => channel.read().unwrap().guild_id,
+    let guild_id = match CACHE.read().guild_channel(msg.channel_id) {
+        Some(channel) => channel.read().guild_id,
         None => {
             check_msg(msg.channel_id.say("Groups and DMs not supported"));
 
@@ -95,8 +95,8 @@ command!(join(ctx, msg, args) {
         },
     };
 
-    let guild_id = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
-        Some(channel) => channel.read().unwrap().guild_id,
+    let guild_id = match CACHE.read().guild_channel(msg.channel_id) {
+        Some(channel) => channel.read().guild_id,
         None => {
             check_msg(msg.channel_id.say("Groups and DMs not supported"));
 
@@ -111,8 +111,8 @@ command!(join(ctx, msg, args) {
 });
 
 command!(leave(ctx, msg) {
-    let guild_id = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
-        Some(channel) => channel.read().unwrap().guild_id,
+    let guild_id = match CACHE.read().guild_channel(msg.channel_id) {
+        Some(channel) => channel.read().guild_id,
         None => {
             check_msg(msg.channel_id.say("Groups and DMs not supported"));
 
@@ -133,8 +133,8 @@ command!(leave(ctx, msg) {
 });
 
 command!(mute(ctx, msg) {
-    let guild_id = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
-        Some(channel) => channel.read().unwrap().guild_id,
+    let guild_id = match CACHE.read().guild_channel(msg.channel_id) {
+        Some(channel) => channel.read().guild_id,
         None => {
             check_msg(msg.channel_id.say("Groups and DMs not supported"));
 
@@ -182,8 +182,8 @@ command!(play(ctx, msg, args) {
         return Ok(());
     }
 
-    let guild_id = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
-        Some(channel) => channel.read().unwrap().guild_id,
+    let guild_id = match CACHE.read().guild_channel(msg.channel_id) {
+        Some(channel) => channel.read().guild_id,
         None => {
             check_msg(msg.channel_id.say("Error finding channel info"));
 
@@ -212,8 +212,8 @@ command!(play(ctx, msg, args) {
 });
 
 command!(undeafen(ctx, msg) {
-    let guild_id = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
-        Some(channel) => channel.read().unwrap().guild_id,
+    let guild_id = match CACHE.read().guild_channel(msg.channel_id) {
+        Some(channel) => channel.read().guild_id,
         None => {
             check_msg(msg.channel_id.say("Error finding channel info"));
 
@@ -231,8 +231,8 @@ command!(undeafen(ctx, msg) {
 });
 
 command!(unmute(ctx, msg) {
-    let guild_id = match CACHE.read().unwrap().guild_channel(msg.channel_id) {
-        Some(channel) => channel.read().unwrap().guild_id,
+    let guild_id = match CACHE.read().guild_channel(msg.channel_id) {
+        Some(channel) => channel.read().guild_id,
         None => {
             check_msg(msg.channel_id.say("Error finding channel info"));