Mullein

Copperbox revision 576.

The code is very rough, but I've got ABC output from a Haskore score (i.e. an interpretation of the Music data type) rather than a performance (an interpretation of the Perfomance datatype).

HNotate only ever interpreted the Performance data type, which was problemmatic (though I can't quite remember why). Also I've decided not to try to reconstruct structure (e.g. chords) in the output. Chords should still be printed by virtue of their notes being over layed at the same time, but they won't be explicit in the generated score.