code: def conference(self, id, **options):
          
          self._steps.append(Conference(id, **options).obj)
docs: This object allows multiple lines in separate sessions to be conferenced together so that the parties on each line can talk to each other simultaneously.
          This is a voice channel only feature.
          Argument: "id" is a String
          Argument: **options is a set of optional keyword arguments.
          See https://www.tropo.com/docs/webapi/conference