Transition from v0.1 XML playlists to v0.2 YAML playlists.

Transition from v0.1 XML playlists to v0.2 YAML playlists.

All test/ tests pass except for tutorial.py and note.py, which take
forever to run.  I'm going to figure out what's going on there next.

Anyone with old playlist files can either upgrade by hand (the new
syntax is pretty simple, see the playlists under test/data/ for
examples), or use the automatic script
  contrib/upgrade_playlist_0p1.py
which converts the playlists automatically.  The output from the
upgrade script is, like most auto-generated files, less concise
than a hand coded playlist, but it will work just fine.

For an introduction to YAML, see
  http://www.yaml.orlg/
which contains links YAML libraries in a number of languages.  The
playlists are generated with PyYAML
  http://pyyaml.org/
which handles YAML 1.1
  http://yaml.org/spec/1.1/
The Hooke playlist format is pretty simple, so it shouldn't be too
strongly tied to any particular version of YAML, although I haven't
actually tested it with a 1.0 or 1.2 parser.