[Vorbis] MARC relators added to Dublin Core

[Ian Malone]

Just noticed this, <http://dublincore.org/usage/documents/relators/>.
MARC (Library of Congress) relators are now part of Dublin Core,
this allows refinements to meta-data like actor, composer,
instrumentalist (of interest to kitchen sink metadata in Ogg/Vorbis).

It still falls short of the more qualified relationships that might
be available with Musicbrainz advanced relationships (eg guitarist
etc), but I feel the Musicbrainz guidelines are still not perfectly
documented.

-- 
imalone