t/gun
            (fun/*/gun/*, sun/foo/bar) -> parent/fun/foo/gun/bar

        Examples
        --------
        For example suppose the source directory contains fun/foo.dat and
        fun/bar/car.dat:

        >>> self.add_data_dir('fun')                       #doctest: +SKIP
        >>> self.add_data_dir(('sun', 'fun'))              #doctest: +SKIP
        >>> self.add_data_dir(('gun', '/full/path/to/fun'))#doctest: +SKIP

        Will install data-files to the locations::

            <package install directory>/
              fun/
                foo.dat
                bar/
                  car.dat
              sun/
                foo.dat
                bar/
                  car.dat
              gun/
                foo.dat
                car.dat

        Nc