Re-implement voice sending.

This is a complete redesign of the old voice code.

A list of major changes is as follows:

* The voice websocket will now automatically reconnect with
  exponential back-off just like the regular Client does.
* Removal of the stream player concept.
* Audio now gracefully pauses and resumes when a disconnect is found.
* Introduce a discord.AudioSource concept to abstract streams
* Flatten previous stream player functionality with the
  VoiceClient, e.g. player.stop() is now voice_client.stop()
* With the above re-coupling this means you no longer have to
  store players anywhere.
* The after function now requires a single parameter, the error,
  if any existed. This will typically be None.

A lot of this design is experimental.

discord/state.py

@@ -688,6 +688,16 @@ class ConnectionState:
             if call is not None:
                 call._update_voice_state(data)
 
+    def parse_voice_server_update(self, data):
+        try:
+            key_id = int(data['guild_id'])
+        except KeyError:
+            key_id = int(data['channel_id'])
+
+        vc = self._get_voice_client(key_id)
+        if vc is not None and vc.is_connected():
+            compat.create_task(vc._switch_regions())
+
     def parse_typing_start(self, data):
         channel = self.get_channel(int(data['channel_id']))
         if channel is not None: