HNotate

Copperbox revision 221.

I've added a new operator to the print representations in HNotate - (<+<).

It's a type restricted version of mappend and it allows parameterized sequences to be built. Previously holes in sequences had to be one element because they could only be built with the addto operator (+++), now holes can themselves be sequences. This will allow HNotate LilyPond to append the notelist it produces to a user supplied initial block that contains key signature, time signature etc.

Disappointingly, these four lines of code (one for the type class, one for the fixity declaration, one for the type signature and one for the implementation) have taken four days work. I convinced myself early on that the current representation wasn't suitable and I'd have to go to something more directly compositional like the Wash HTML representation, then spent a lot of time getting lost.