Implement AutoShardedClient for transparent sharding.

This allows people to run their >2,500 guild bot in a single process
without the headaches of IPC/RPC or much difficulty.

discord/http.py

@@ -588,5 +588,14 @@ class HTTPClient:
             raise GatewayNotFound() from e
         return data.get('url') + '?encoding=json&v=6'
 
+    @asyncio.coroutine
+    def get_bot_gateway(self):
+        try:
+            data = yield from self.get(self.GATEWAY + '/bot', bucket=_func_())
+        except HTTPException as e:
+            raise GatewayNotFound() from e
+        else:
+            return data['shards'], data['url'] + '?encoding=json&v=6'
+
     def get_user_info(self, user_id):
         return self.get('{0.USERS}/{1}'.format(self, user_id), bucket=_func_())