[Playlist] xspf resolver

[Lucas Gonze]

>>         o Extract out the track, artist, album and musicbrainz ID from
>>           the musicbrainz DOM
>>         o Insert (or replace) the proper field in the XSPF DOM, as
>>           well as a comment to indicate which fields have been added
>>           or change
>>   * Output the updated XSPF

The last step: convert each Musicbrainz reference into a fetchable 
resource, like an iTunes store song URL or a path in the local filesystem.

Now, that's actually pretty easy.  In fact, it's *really really* easy, 
since Musicbrainz has a wealth of tools for converting song files into 
Musicbrainz IDs.  All you have to do is run the Musicbrainz tagger against 
your local collection and save the results in a catalog to compare against 
the return results of your web service.

Wow.  I can't believe it's that easy.

One request -- when you're inserting fields into the DOM, can you provide 
a //playlist/trackList/track/identifier field with the permanent URI of 
the song on Musicbrainz.org?  That ID can perform a ton of work down the 
road, as the playlist gets passed around.