The old build system worked, but ssg adds some features while still
being simple and easy to hack on:
* set page title from the h1 tag, rather than the file name
* generate a sitemap (which we adapt to also generate a nav)
This site doesn't need a dynamic nav, but the Anarchy Planet docs site
will have a lot of rapidly changing pages and will benefit from a
dynamic nav. This way we can use the same build system for both
sites.
Lowdown is fairly simple while supporting the PHP Extra extensions.
It also comes with extensive documentation in its man pages, for example
the whole language is described in lowdown(5).
See https://kristaps.bsd.lv/lowdown/
This fixes a big TODO (anchor links for the table of contents on the
webring page).
