Return the splits of the activity with the given id.

        :param unit: The unit to use for splits. May be one of
                      'mi' or 'km'.

def get_splits(self, id_num, unit='mi'):
        """Return the splits of the activity with the given id.

        :param unit: The unit to use for splits. May be one of
                      'mi' or 'km'.

        """
        url = self._build_url('my', 'activities', id_num, 'splits', unit)

        return self._json(url)