HNotate

Copperbox revision 264.

A major update - I've now made both the Abc and LilyPond parsers do the 'island parsing' in a preprocessing step. This has made them much simpler - and both can use the exprView parser which parses the shape of a post-processed view .

Also the evaluation of a post-processed view has been simplified in OutputMain. Post-processed LilyPond and Abc are both represented as a very simple datatype Expr which has a handy use of higher-order abstract syntax to modify the environment as Expr is being traversed.