Neume

Copperbox revision 1257.

I've moved the modules AbcFormat and LilyPondFormat from Extra to Core. This means that simple scores (i.e. ones with only notes, not percussion or guitar chords) can work by importing modules from Neume.Core to ABC or LilyPond only, though they will miss e.g. all the named notes.

This was the intention when I moved some code out into Extra in the first place - however as I was developing, some code didn't naturally fit this distinction. Now that I've much of the work prototyped at least, its easier to see where things should go.