Add genre support using musicbrainz tags.

Author: aereaux

beets/autotag/mb.py

@@ -70,7 +70,7 @@ def get_message(self):
 RELEASE_INCLUDES = ['artists', 'media', 'recordings', 'release-groups',
                     'labels', 'artist-credits', 'aliases',
                     'recording-level-rels', 'work-rels',
-                    'work-level-rels', 'artist-rels']
+                    'work-level-rels', 'artist-rels', 'genres']
 TRACK_INCLUDES = ['artists', 'aliases']
 if 'work-level-rels' in musicbrainzngs.VALID_INCLUDES['recording']:
     TRACK_INCLUDES += ['work-level-rels', 'artist-rels']
@@ -415,6 +415,9 @@ def album_info(release):
         first_medium = release['medium-list'][0]
         info.media = first_medium.get('format')
 
+    if release.get('genre-list'):
+        info.genre = sorted(release['genre-list'], key=lambda x: x['count'])[-1]["name"]
+
     info.decode()
     return info