Add Channel.voice_members

This allows you to see which members are currently in a voice
channel.

discord/channel.py

@@ -56,10 +56,15 @@ class Channel(object):
 
         An array of :class:`Roles` that have been overridden from their default
         values in the :attr:`Server.roles` attribute.
+    .. attribute:: voice_members
+
+        An array of :class:`Members` that are currently inside this voice channel.
+        If :attr:`type` is not ``'voice'`` then this is always an empty array.
     """
 
     def __init__(self, **kwargs):
         self.update(**kwargs)
+        self.voice_members = []
 
     def update(self, **kwargs):
         self.name = kwargs.get('name')