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/__init__.py

@@ -19,8 +19,8 @@ __version__ = '1.0.0a'
 
 from .client import Client, AppInfo
 from .user import User, ClientUser, Profile
-from .game import Game
 from .emoji import Emoji, PartialEmoji
+from .activity import *
 from .channel import *
 from .guild import Guild
 from .relationship import Relationship