Fork and add a copy of Tom Johnson's Jekyll Documentation Theme

It's time to make a version of the [Documentation theme](https://github.com/tomjoht/documentation-theme-jekyll) that works well with AsciiDoc and LiquiDoc.

One idea is to make a converter, which would rename directories, insert some files, but otherwise fall back on the prime version. But it's more likely the best idea to maintain a proper fork, as some modifications we would make sense to contribute back, even if the overhaul is pretty thorough. We may keep it as an optional branch of this repo, so users can choose a bare-bones LDCMF and code their own theme, or they can stay in sync with the latest boilerplate edition of this theme, and maybe later others as well.