Add a section listing priority efforts. Ensure that there is
exactly one spec listed for each priority effort. Add stub specs
for efforts which predate the spec process. Also, publish the
Gerrit search string to see all priority effort changes.
Remove the implemented/ directory so that spec URLs are stable
over time. We have been linking to them very liberally, so let's
not codify workflow in URLs.
Remove the :glob: options so that specs now need to be listed
individually in the sections in which they should appear. This
means that spec workflow involves changing the index page rather
than moving files (and URLs).
Change-Id: Ic7f088b7456d66f5ff164dea8504e1c5467bf79d
