docs: def stop(self, historics_id, reason=''):
          """ Stop an existing Historics query.
  
              Uses API documented at http://dev.datasift.com/docs/api/rest-api/endpoints/historicsstop
  
              :param historics_id: playback id of the job to stop
              :type historics_id: str
              :param reason: optional reason for stopping the job
              :type reason: str
              :return: dict of REST API output with headers attached
              :rtype: :class:`~datasift.request.DictResponse`
              :raises: :class:`~datasift.exceptions.DataSiftApiException`, :class:`requests.exceptions.HTTPError`
          """
          return self.request.post('stop', data=dict(id=historics_id, reason=reason))