Implement VoiceProtocol lower level hooks.

This allows changing the connect flow and taking control of it without
relying on internal events or tricks.

discord/ext/commands/context.py

@@ -238,7 +238,7 @@ class Context(discord.abc.Messageable):
 
     @property
     def voice_client(self):
-        r"""Optional[:class:`.VoiceClient`]: A shortcut to :attr:`.Guild.voice_client`\, if applicable."""
+        r"""Optional[:class:`.VoiceProtocol`]: A shortcut to :attr:`.Guild.voice_client`\, if applicable."""
         g = self.guild
         return g.voice_client if g else None