That is, in addition to contributing to the distance function, the plugin can
also influence the initial search into MusicBrainz. This will allow albums to be
tagged even when they're missing metadata entirely. This change required a
significant bit of refactoring to the "mb" module -- it's much nicer now.
This involves yet another new plugin method: album_distance. This leaves as the
last major puzzle piece for lastid the ability to augment the initial search
into MB (i.e., can start a search using fingerprinted metadata).
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).
