Used to register handler at the dispatcher.

        :param alias: Signal alias to match handler to.
        :param handler: Handler. Some callable.
        :return:

def register_handler(alias: str, handler: callable):
        """
        Used to register handler at the dispatcher.

        :param alias: Signal alias to match handler to.
        :param handler: Handler. Some callable.
        :return:
        """
        if SignalDispatcher.handlers.get(alias) is None:
            SignalDispatcher.handlers[alias] = [handler]
        else:
            SignalDispatcher.handlers.get(alias).append(handler)