Neume

Copperbox revision 1128.

Mullein M2 is now called Neume. The name is meant to indicate that Neume is a somewhat primitive system for music scores.

I've changed the syntax in this commit - staff syntax (the complicated one with beam groups, tuplets, chords and grace notes) is in a distinct module to markup (the simpler one for chord diagrams etc.) and doc syntax (for post processing after rendering to ABC or LilyPond, e.g. adding bar lines, repeats...).