HNotate

Copperbox revision 220.

I've tidied up the phantom type layer for the Abc and LilyPond pretty printers. The 'Skeleton Doc' has gone and both libs now share the same code for appending and attributing elements.

This removes one of the 'sore thumbs' of HNotate, there are plenty of others as the code has been written quickly and revised often so is particularly ragged (and there are some holes where I haven't re-implemented features that were 'revised-out').

There are also some stumbling blocks that stop it being generally usefully, big ones are:
- What to do about 'systems' i.e. multiple staves - really the renderers should be open so the user can control this.
- What to do about glyphs that aren't notes or rests - currently there is no way to get say, expression marks, into the score output.