Bala

Copperbox revision 179.

Added a new output representation for Abc. This one is patterned after the Text.XHTML library in the hierarchical libraries - with a phantom type layer to have comparable 'typefulness' to the SymAbc representation.

Unlike SymAbc it doesn't generate abstract syntax, instead it goes almost* straight to the pretty printers Doc type. While this makes it more limited than SymAbc it does represent Abc with workable types - SymAbc's types were too big to program with.

--

* The new library has a skeleton syntax layer above the Doc type, but this seems unnecessary and may be removed in due course.