Parse the DCAP-AP.de license vocabulary to generate a build representation of common licenses.

Created by: adamreichold

Using meta programming might be nice to include a compile-time representation of the official DCAT-AP.de vocabulary. On the other hand, this might not be worth as these license identifiers seem to be in rather ad-hoc manners, i.e. it would be more important to be lenient than to have a closed representation.

For example, on opendata.leipzig.de, the license is consistently identified by dl-de-by-2.0 instead of dl-by-de/2.0. Hence parsing would need to be much more flexible than just implementing the DCAT-AP.de vocabulary in any case. (But this could for example be handled by a list of license identifier synonyms.)

(It is somewhat unfortunate to have a second XML parser as a build dependency, but it is only a build dependency and quick-xml with serde cannot disambiguate the namespaced XML tags used by the DCAP-AP.de RDF files.)