Change all change notes to reference the filename of the tune to change to.
Modify web and document generators to pull the change note out of the abc
and generate an appropiate bit of content. This is now, in both cases,
a hyperlink.
In the process, remove the tune-specific .tex facility. It wasn't being
used.
I could really do with a proper templating system, and using some sort
of templating in the LaTeX generation.
The aim of MIDI and MP3 is to allow the user to hear what a tune sounds
like. For transposed bookes, I think this should be reused from the main
booke page, because hearing it at the transposed pitch isn't a major help.
And in fact given the way cello transposition is done, the sound won't
be transposed anyway. And Jane hasn't complained.
This will speed up building the bookes by removing audio generation,
the slowest process, from the transposed bookes.