Add graceful exits

This sets up a set of ropes and pulleys that signal the `Bot.keepalive`
function to clean things up after a quit signal has been sent. This
allows plugins to define an `on_unload` function to save any important
datas on intentional exit.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

omnibot/bot.py

@@ -22,6 +22,7 @@ class Bot:
         ]
         # TODO - this may not be needed
         self.__channels: Set[str] = set()
+        self.__quitting = asyncio.Event()
 
     @property
     def server_config(self) -> ServerConfig:
@@ -31,6 +32,9 @@ class Bot:
     def plugins(self) -> Sequence[plugin.Plugin]:
         return self.__plugins
 
+    def quit(self):
+        self.__quitting.set()
+
     def channel_plugins(self, channel: str) -> Sequence[plugin.Plugin]:
         return [plugin for plugin in self.plugins if channel in plugin.channels]
 
@@ -127,6 +131,9 @@ class Bot:
 
     async def keepalive(self):
         # loop while we're connected, check every second
-        log.info("Starting keepalive loop")
-        while self.connection.connected:
-            await asyncio.sleep(1.0)
+        await self.__quitting.wait()
+        log.info("Shutting down gracefully")
+        # TODO: unload modules
+        await asyncio.gather(
+            *[plugin.on_unload(self.connection) for plugin in self.plugins]
+        )