Neume

Copperbox revision 1221.

Work towards overlays (parallel music) for LilyPond.

LilyPond is significantly harder candidate for overlays than ABC. Rendering can be stateful - so I sometimes must use stmap rather than fmap. Also overlays can have different types i.e. one overlay line can be guitar chords and one normal notes. I'm committing the current work even though it is a way of working, as its in danger of getting complicated, ad hoc very quickly.