HNotate

Copperbox revision 296.

Some work on annotations. I've put in a mechanism where Abc annotations are dropped for LilyPond output and vice versa.

This fits with a principle I have for HNotate where you have a canonical notelist but might choose to render it differently (i.e. as Abc or LilyPond), but it needs some more thought. The important thing about annotations is that they let you get to the 'good stuff' in LilyPond (e.g. dynamic markings, string numbering for tablature output etc.). One of the things I want to be able to do is render a tune both as staff notation and guitar tablature, and I don't want the same annotations in both. The annotation mechanism in HNotate will need a finer grained notion of context than just Abc/LilyPond.