Starts this bot in a separate thread. Therefore, this call is non-blocking.

        It will listen to all new submissions created in the :attr:`~subreddits` list.

def start(self):
        """
        Starts this bot in a separate thread. Therefore, this call is non-blocking.

        It will listen to all new submissions created in the :attr:`~subreddits` list.
        """
        super().start()
        submissions_thread = BotThread(name='{}-submissions-stream-thread'.format(self._name),
                                       target=self._listen_submissions)
        submissions_thread.start()
        self._threads.append(submissions_thread)
        self.log.info('Starting submissions stream ...')