Add initial audio support

Audio can be played with support by passing one of the following into
the `Handler::play` method:

`serenity::ext::voice::{ffmpeg, pcm, ytdl}` functions, where
- `ffmpeg` accepts a path (such as a `File`);
- `pcm` accepts a raw reader source;
- `ytdl` accepts a URI, which works with everything youtube-dl supports:
  <https://github.com/rg3/youtube-dl/blob/master/docs/supportedsites.md>

The source can be stopped via [`Handler::stop`].

Receive is supported through [`Handler::listen`], which accepts a
`serenity::ext::voice::AudioReceiver` implementation.

An example is provided in the form of the file located at
`./examples/07_voice.rs`, which can be run by cloning the repo and
performing the command `cargo run --example 07_voice`. Prior to running
the command, set a bot token as the value of the env variable
`DISCORD_TOKEN`. The example supports:

- `deafen`: deafens the bot;
- `join`: joins a voice channel by ID. The example is a primitive
  implementation, and requires the ID of the channel to be passed to the
  bot as a command of `~join 131937933270712320`;
- `leave`: leaves the current voice channel, if in one;
- `mute`: mutes the bot and will continue to play source audio;
- `play`: plays source audio from a URI, through a command like
  `~play https://www.youtube.com/watch?v=5KJjBRm0ElA`;
- `ping`: responds with "Pong!" to ensure the bot is working properly;
- `undeafen`: undeafens the bot, if that's actually a word;
- `unmute`: unmutes the bot.

Documentation for audio can be found at:

<https://serenity.zey.moe/serenity/ext/voice/index.html>

1 files changed, 9 insertions, 14 deletions

diff --git a/src/model/voice.rs b/src/model/voice.rs
index a888029..61035c6 100644
--- a/src/model/voice.rs
+++ b/src/model/voice.rs
@@ -4,16 +4,7 @@ use ::constants::VoiceOpCode;
 use ::internal::prelude::*;
 use ::utils::decode_array;
 
-#[derive(Clone, Debug)]
-pub struct VoiceHandshake {
-    pub heartbeat_interval: u64,
-    pub ip: Option<String>,
-    pub modes: Vec<String>,
-    pub port: u16,
-    pub ssrc: u32,
-}
-
-#[derive(Clone, Debug)]
+#[derive(Clone, Copy, Debug)]
 pub struct VoiceHeartbeat {
     pub heartbeat_interval: u64,
 }
@@ -21,6 +12,7 @@ pub struct VoiceHeartbeat {
 #[derive(Clone, Debug)]
 pub struct VoiceHello {
     pub heartbeat_interval: u64,
+    pub ip: String,
     pub modes: Vec<String>,
     pub port: u16,
     pub ssrc: u32,
@@ -32,7 +24,7 @@ pub struct VoiceReady {
     pub secret_key: Vec<u8>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Copy, Debug)]
 pub struct VoiceSpeaking {
     pub speaking: bool,
     pub ssrc: u32,
@@ -41,7 +33,6 @@ pub struct VoiceSpeaking {
 
 #[derive(Clone, Debug)]
 pub enum VoiceEvent {
-    Handshake(VoiceHandshake),
     Heartbeat(VoiceHeartbeat),
     Hello(VoiceHello),
     Ready(VoiceReady),
@@ -56,16 +47,20 @@ impl VoiceEvent {
         let op = req!(try!(remove(&mut value, "op")).as_u64());
         let mut map = try!(remove(&mut value, "d").and_then(into_map));
 
-        match try!(VoiceOpCode::from_num(op).ok_or(Error::Client(ClientError::InvalidOpCode))) {
+        let opcode = try!(VoiceOpCode::from_num(op)
+            .ok_or(Error::Client(ClientError::InvalidOpCode)));
+
+        match opcode {
             VoiceOpCode::Heartbeat => {
                 missing!(map, VoiceEvent::Heartbeat(VoiceHeartbeat {
-                    heartbeat_interval: req!(try!(remove(&mut value, "heartbeat_interval")).as_u64()),
+                    heartbeat_interval: req!(try!(remove(&mut map, "heartbeat_interval")).as_u64()),
                 }))
             },
             VoiceOpCode::Hello => {
                 missing!(map, VoiceEvent::Hello(VoiceHello {
                     heartbeat_interval: req!(try!(remove(&mut map, "heartbeat_interval"))
                         .as_u64()),
+                    ip: try!(remove(&mut map, "ip").and_then(into_string)),
                     modes: try!(decode_array(try!(remove(&mut map, "modes")),
                                              into_string)),
                     port: req!(try!(remove(&mut map, "port"))