Invoke the bot callback in an async wrapper.

Hopefully, should stop plugins blocking the async thread.

errmatrix.py

@@ -234,7 +234,7 @@ class MatrixBackendAsync(object):
                 err_room
             )
             self._annotate_event( event, msg.extras )
-            self._bot.callback_message( msg )
+            await self._bot.loop.run_in_executor(None, self._bot.callback_message, msg)
         except Exception as e:
             log.warning("something went wrong processing a message... %s", e)
             import traceback
@@ -299,7 +299,6 @@ class MatrixBackendAsync(object):
             raise Exception("couldn't create management room")
 
 
-
     async def send_message(self, msg: backend.Message) -> None:
         """Send a errbot-style message to matrix"""