cfbot update: Using GitHub for patch review

I recently got write access to the cfbot repo[1] and machine from
Thomas. And I deployed a few improvements this week. The most
significant one is that it is now much easier to use GitHub as part of
your patch review workflow.

On the cfbot website[2] there's now a "D" (diff) link next to each
commit fest entry. A good example of such a link would be the one for
my most recent commitfest entry[3]. There is a separate commit for
each patch file and those commits contain the "git format-patch"
metadata. (this is not done using git am, but using git mailinfo +
patch + sed, because git am is horrible at resolving conflicts)

The killer feature (imho) of GitHub diffs over looking at patch files:
You can press the "Expand up"/"Expand down" buttons on the left of the
diff to see some extra context that the patch file doesn't contain.

You can also add the cfbot repo as a remote to your local git
repository. That way you don't have to manually download patches and
apply them to your local checkout anymore:

# Add the remote
git remote add -f cfbot https://github.com/postgresql-cfbot/postgresql.git
# make future git pulls much quicker (optional)
git maintenance start
# check out a commitfest entry
git checkout cf/5065

P.S. Suggestions for further improvements are definitely appreciated.
We're currently already working on better integration between the
commitfest app website and the cfbot website.

P.P.S The "D" links don't work for patches that need to be rebased
since before I deployed this change, but that problem should fix
itself with time.

[1]: https://github.com/macdice/cfbot
[2]: http://cfbot.cputube.org/
[3]: https://github.com/postgresql-cfbot/postgresql/compare/cf/5065~1...cf/5065