Merge branch 'ps/build-meson-html'

The build procedure based on meson learned to generate HTML
documention pages.

* ps/build-meson-html:
  Documentation: wire up sanity checks for Meson
  t/Makefile: make "check-meson" work with Dash
  meson: install static files for HTML documentation
  meson: generate articles
  Documentation: refactor "howto-index.sh" for out-of-tree builds
  Documentation: refactor "api-index.sh" for out-of-tree builds
  meson: generate user manual
  Documentation: inline user-manual.conf
  meson: generate HTML pages for all man page categories
  meson: fix generation of merge tools
  meson: properly wire up dependencies for our docs
  meson: wire up support for AsciiDoctor