Convert files to zip archive.
        :return: None
        :rtype: :py:obj:`None`

def _to_zipfile(self, file_generator):
        """Convert files to zip archive.
        :return: None
        :rtype: :py:obj:`None`
        """
        with zipfile.ZipFile(file_generator.to_path, mode="w", compression=zipfile.ZIP_DEFLATED) as outfile:
            for f in file_generator:
                outpath = self._output_path(f.source, file_generator.to_format, archive=True)
                outfile.writestr(outpath, f.writestr(file_generator.to_format))