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.
This is done by
a) reducing the page margins
b) compressing the heading and removing all but Notes: fields.
The latter produced vertically smaller tune PDFs that will scale wider.
In the process, modify abctitle.py to extract the first of any header field, and
move formatting for a single tune into a .fmt file.