Emit a custom event to one or more connected clients.

def emit(self, event, data=None, room=None, include_self=True,
             namespace=None, callback=None):
        """Emit a custom event to one or more connected clients."""
        return self.socketio.emit(event, data, room=room,
                                  include_self=include_self,
                                  namespace=namespace or self.namespace,
                                  callback=callback)