HNotate

Copperbox revision 377.

Work to add templates for Midi output, so Midi would work like LilyPond or Abc...

However, its probably Midi's swan song as far as HNotate goes. I think I can say that having HNotate work with both Abc and LilyPond has improved HNotate. While there is still plenty of convoluted code in HNotate, targeting both Abc and LilyPond has made me look for better solutions than I think I would have found just targeting LilyPond. But, I believe that adding Midi support has made HNotate worse - to support Midi it feels like I've dubiously generalized some parts of HNotate that supported Abc and HNotate well. So after this revision I think Midi's time is up.

I'd like to add a notelist backend at some point that can easily be parsed and turned into Midi (something like one of the Humdrum representations), but a representation that is still textual so better matches what HNotate is good at.