Add/enable stub man reference

This doesn't generate anything interesting, but it sets up the infrastructure
for generating man pages along with all the other references.
Broken commit: move old man updater from rakefile to man reference

This is just a starting point.
Add Ronn to Gemfile
Show how to get the names of all applications and faces

(We're just dumping them to a file, here)
Write mixture of processed and unprocessed man pages

Processing applications, not processing faces. Gonna unify these next.
Unify piping things through ronn

Alas, ronn doesn't seem to have a usable Ruby API, so we'll just pipe through
it. Waste of cycles, but whatever, I'm trying to do the minimum to get this
working.
Categorize subcommands and write an index page

This is a revised commit; in the original version, puppet config was in
occasional (moved to niche because it doesn't currently work) and puppet
plugin was in niche (moved to occasional, since doing a pluginsync with no
catalog is sometimes helpful).
Stop dumping the application names to a file
De-dupe man pages link in the per-version references index
Use a separate nav snippet for man page references, because relative links

This sidebar system gets jankier every day. Sorry, future self!
Allow building references with unreleased Puppet versions (VERSION=x.x.x COMMIT=abc0567)

We've run into this annoyance a few times, where we know what's going into the
coming version but we can't generate the references until the release is tagged.
Makes previewing a bit of a pain.

Long story short, we were being authoritarian about validating things without
providing an override. So here's the override: if you provide both VERSION and
COMMIT environment variables, the reference generator will check out the commit
instead of locking you to a tag.
Delete extraneous "fetch_tags" task

This task was A: unnecessary (we fetch updates and do checkouts in the
PuppetDocs code) and B: obstructive (if the puppet directory wasn't already a
git repo, rake references would refuse to run, so we had a bootstrapping problem
if you'd never generated references before).
Regenerate references for 3.4.0-rc1

* Build man pages! Let's make 3.4 the maiden voyage for this boat.
* Regenerate yard docs. Turns out if you use `rake references` instead of `bundle
  exec rake references`, it'll use the wrong yard version and format things
  in a wack fashion.
Merge branch 'manpage_redux'