UCD resolver

The UCD resolver uses the metadata in the current Registry to suggest UCDs pertinent to natural language column descriptions. In that, it fulfills a similar function as the `CDS UCD builder`_ but uses an entirely different approach. .. _CDS UCD builder: http://cdsweb.u-strasbg.fr/UCD/cgi-bin/descr2ucd
Natural-language description of the column contents. Remove terms if you get no matches.