This significantly speeds up our doc build process. This requires a
newer version of 'sphinx-feature-classification' and some tweaks to our
own in-tree extensions. While we're here, we drop the '-d DOCTREE_DIR'
parameter since it's of no use when we blast away our previously built
docs each time we build.
Change-Id: I679da65d44c40880f720df8a2f06286a19eb8d22
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
7062e1db8b