Import a Milestone and returns a :class:`Milestone` object.

        :param name: name of the :class:`Milestone`
        :param estimated_start: estimated start time of the
                                :class:`Milestone`
        :param estimated_finish: estimated finish time of the
                                 :class:`Milestone`
        :param attrs: optional attributes for :class:`Milestone`

def import_milestone(self, name, estimated_start, estimated_finish,
                         **attrs):
        """
        Import a Milestone and returns a :class:`Milestone` object.

        :param name: name of the :class:`Milestone`
        :param estimated_start: estimated start time of the
                                :class:`Milestone`
        :param estimated_finish: estimated finish time of the
                                 :class:`Milestone`
        :param attrs: optional attributes for :class:`Milestone`
        """
        return Milestones(self.requester).import_(
            self.id, name, estimated_start,
            estimated_finish, **attrs
        )