This required the introduction of a track_distance method on plugins. We'll also
need to add an album_distance method as well as a mechanism for extending the
search routine (so we can search for albums in MusicBrainz even when they have
no tags). This commit also adds the '-v' flag for printing debug logs (something
we should do more of).
This makes way more sense than fetching every metadata request from the
database. The performance of "beet ls -a" and the like should be drastically
better.
As part of this, the BaseLibrary class was also adapted to include a notion of
albums. This is reflected by the new BaseAlbum class, which the Album class
(formerly _AlbumInfo) completely replaces in the concrete Library. The BaseAlbum
class just fetches metadata from the underlying items.
