HNotate

Copperbox revision 258.

I've added an initial mechanism for pitch name naturalization to the Abc output so that accidentals aren't printed when they are already accounted for by the key signature. So far this is only done for two keys as I'm not sure whether to enumerate all the keys 'by hand' or take some of the interval code from Bala and construct the pitch spellings from interval patterns.

The Abc output still doesn't calculate durations properly as this is more involved than with LilyPond, that looks like the next thing to do.