Search for albums and tracks by name

This is a *work in progress* especially since I haven't written enough tests.  I'd be interested in the API approach. Specifically is `search_tracks` enough?  I found it easier to have simpler routines that let you return albums and tracks which is why I added `get_albums_for_artist` and `get_tracks_for_album` too.

The code *does* work since I've used this to search for a bunch of music library tracks automatically.  Took a while to get the Unicode and URL encoding working especially from py2.6 to 3.x.  I added a new compatibility call quote_path from urllib or urllib.parse (py3) that is used by new utility function `url_escape_path`. 

I'd recommend to add a doctest here, to illustrate what the method does.