Merge branch 'ps/meson-build-docs'

Merge branch 'ps/meson-build-docs'

The build procedure based on meson learned a target to only build
documentation, similar to "make doc".

* ps/meson-build-docs:
  ci: don't compile whole project when testing docs with Meson
  meson: print docs backend as part of the summary
  meson: introduce a "docs" alias to compile documentation only