Mullein

Copperbox revision 692.

I've started a branch of Mullein, to experiment with simplifying the internal syntax.

I don't like how Mullein represents musically structures larger than a bar as motifs, phrases and parts. These structures are pretty arbitrary, so it seems better to do away with them altogether and somehow print structure with functions - at its simplest this will mean adding functions to print sequences of bars and repeats. Also within a bar it would be nice to avoid the overlay syntax if the particular score doesn't use then, so I want to try and make overlays optional.