Split Game object to separate Activity subtypes for Rich Presences.

This is a massive breaking change.

* All references to "game" have been renamed to "activity"
* Activity objects contain a majority of the rich presence information
* Game and Streaming are subtypes for memory optimisation purposes for
  the more common cases.
* Introduce a more specialised read-only type, Spotify, for the
  official Spotify integration to make it easier to use.

discord/guild.py

@@ -32,7 +32,7 @@ from collections import namedtuple, defaultdict
 from . import utils
 from .role import Role
 from .member import Member, VoiceState
-from .game import Game
+from .activity import create_activity
 from .permissions import PermissionOverwrite
 from .colour import Colour
 from .errors import InvalidArgument, ClientException
@@ -243,8 +243,7 @@ class Guild(Hashable):
             member = self.get_member(user_id)
             if member is not None:
                 member.status = try_enum(Status, presence['status'])
-                game = presence.get('game', {})
-                member.game = Game(**game) if game else None
+                member.activity = create_activity(presence.get('game'))
 
         if 'channels' in data:
             channels = data['channels']