Add Client.clear to clear the bot's internal state to a clean slate.

In case you want to have some external restart loop.

discord/client.py

@@ -462,6 +462,18 @@ class Client:
         yield from self.http.close()
         self._ready.clear()
 
+    def clear(self):
+        """Clears the internal state of the bot.
+
+        After this, the bot can be considered "re-opened", i.e. :meth:`.is_closed`
+        and :meth:`.is_ready` both return ``False`` along with the bot's internal
+        cache cleared.
+        """
+        self._closed.clear()
+        self._ready.clear()
+        self._connection.clear()
+        self._http.recreate()
+
     @asyncio.coroutine
     def start(self, *args, **kwargs):
         """|coro|

discord/http.py

@@ -102,6 +102,10 @@ class HTTPClient:
         user_agent = 'DiscordBot (https://github.com/Rapptz/discord.py {0}) Python/{1[0]}.{1[1]} aiohttp/{2}'
         self.user_agent = user_agent.format(__version__, sys.version_info, aiohttp.__version__)
 
+    def recreate(self):
+        if self._session.closed:
+            self._session = aiohttp.ClientSession(connector=self.connector, loop=self.loop)
+
     @asyncio.coroutine
     def request(self, route, *, header_bypass_delay=None, **kwargs):
         bucket = route.bucket