feature request : handling instruments and instrumentists

[eseb63]

i said a generic solution for the tags, to avoid having to create as many tags as instruments in the collection.

but i didn't mean a generic solution for minimserver : minimserver handles by default some entities like Album, AlbumArtist, Artist, Composer, Genre and several others but not instrument, while instrument is, conceptually speaking, in relation with composer, artist, work, genre, track...

so, the need is just to add this missing feature, the handling of which could be specific ?