Improve documentation generation

Improve documentation generation

• Update Les·M·L to 0.4.0.

• Switch to using a local transform, `xslt/documentation.xslt´, which
includes the Les·M·L parser instead of using the Les·M·L parser
directly. This offers a great deal more configurability and the
potential for customization. Styling information is moved into this
transform and expanded. `<html:i>´ inside of `<html:code>´ is replaced
with `<html:var>´, unless it has a language tag.

• Automatically provide syntax hiliting to code blocks generated from
header files. It¦s impossible to do this perfectly, but assuming files
follow a consistent style, this should handle most cases transparently.
It would be good to document what exactly “consistent style” means.

⋯ More generally, it might be worth extracting this documentation
generation code (and maybe some stuff in `cgirls.mak´ as well?) out
into a separate repository of C tools, but this work will probably be
deferred until there is a second C repository which actually needs to
make use of it.

• Update the markup, and some text, in those documentation comments in
`request.h´.