Subscribe to a topic for receiving events.

        Replace :meth:`autobahn.wamp.interface.IApplicationSession.subscribe`

def subscribe(self, handler, topic=None, options=None):
        """Subscribe to a topic for receiving events.

        Replace :meth:`autobahn.wamp.interface.IApplicationSession.subscribe`
        """
        def proxy_handler(*args, **kwargs):
            return self._callbacks_runner.put(partial(handler, *args, **kwargs))
        return self._async_session.subscribe(proxy_handler, topic=topic, options=options)