AlbumMatch and TrackMatch types

These new named tuples will represent candidates given by the autotagging
system. In the case of album matches, these are currently unwieldy,
verbosely-documented tuples that will only get more unwieldy with the addition
of "unmatched tracks".

beets/autotag/hooks.py

@@ -14,11 +14,14 @@
 
 """Glue between metadata sources and the matching logic."""
 import logging
+from collections import namedtuple
+
 from beets import plugins
 from beets.autotag import mb
 
 log = logging.getLogger('beets')
 
+
 # Classes used to represent candidate options.
 
 class AlbumInfo(object):
@@ -117,6 +120,11 @@ class TrackInfo(object):
         self.disctitle = disctitle
         self.artist_credit = artist_credit
 
+AlbumMatch = namedtuple('AlbumMatch', ['distance', 'info', 'mapping',
+                                       'extra_items', 'extra_tracks'])
+
+TrackMatch = namedtuple('TrackMatch', ['distance', 'info'])
+
 
 # Aggregation of sources.