void mobi_free_opf_spine(OPFspine *spine) {
    if (spine) {
        mobi_free_opf_array(spine->itemref);
        free(spine->toc);
        free(spine);
    }
}
void mobi_free_opf_spine(OPFspine *spine) {
    if (spine) {
        mobi_free_opf_array(spine->itemref);
        free(spine->toc);
        free(spine);
    }
}