.cpu -> html generator

[Doug Evans]

fyi, I've started on a .cpu -> html generator.
The goal is to print human-readable versions of the .cpu files
that can be accessable from the website.
There's lots of todos, no claim is made that it's close to being finished.
See the top of html.scm.

Note: I'd like to set up a nightly or weekly cron job that
generated docs for all the .cpu files.
I'd also like to be able to edit the cgen web pages to refer
to the generated docs, as well as provide documentation that
can be linked to from the generated docs.