Improved iTunes/MP4 (.m4a) tag mappings
Renamed iTunes/MP4 native tags from 'm4a' to 'iTunes MP4'; #13.
Combined unit test for MusicBrainz, to test common mapping using various input formats.
Renamed iTunes/MP4 native tags from 'm4a' to 'iTunes MP4'; #13.
Combined unit test for MusicBrainz, to test common mapping using various input formats.