* scipts/build_*_map.py: Implement helper pythonic scripts used to
generate some Unicode search maps and data for helper Unicode
functions used in MD4C.
This should simplify updating to future Unicode versions.
* md_get_unicode_fold_info: Use data generated by the scripts.
* md_is_unicode_whitespace__: Ditto.
* md_is_unicode_punct__: Ditto.