convert-ly madness on git

[Graham Percival]

Sorry for today's confusion on git, guys.  I was trying to teach
Carl how to do syntax updates, but I'd never actually done it
myself, so there were issues.

Things were complicated by my setup:
- at home, I can commit, but can't compile (so no new convert-ly)
- on GDP, I compile, but can't commit

The good news is that, after one more commit from Carl updating
musicexp.py (musicxml2ly), everything should be fine.  I'll do
another build-from-scratch on GDP to check it.

Other good news is that Carl's had a great crash course on input/ and
the related makefiles, so that's one less piece of (mostly-flawed)
information that might otherwise get lost when I leave.


This will hopefully be the last syntax changes before 2.12, so
after this I shouldn't have problems compiling docs at home again.

Cheers,
- Graham