Rename `documentation` to `documentation.old`

This commit is in preparation for syncing our docs up with the ones
in the `puppet-docs` repo.  Just to make the git history a bit
easier to follow, I've renamed the docs directory to `documentation.old`;
the next commit will add the new docs from the other repo, and then
I'll delete the `old` directory in a final commit.
Copy latest docs from `puppet-docs` repo

We'd like for the docs in the puppetdb repo to always be up-to-date
with the latest code.  However, we also need to keep things in sync
with the documentation team and have a relatively sane way of
publishing the docs to the website.  We'd gotten pretty far out
of sync, so we just went through a process of merging all of the
latest diffs from our docs into the `puppet-docs` repo and reorganizing
things a bit over there.  This commit just copies in the result of that
work into our repo.

Going forward, all docs changes will be made here, and then when we're ready
to publish docs for a new release we'll just copy the whole docs folder
from here to a new, versioned subfolder in the `puppet-docs` repo.
Remove old documentation from repo

Now that we've synced up with the docs in the `puppet-docs` repo,
that version of our docs is the one we'll be maintaining going
forward.  This commit just gets rid of the old version.

Doing this in an isolated commit in hopes of making the git history
a bit easier to follow.
Transform README into more of a table-of-contents

The README had gotten extremely long, and in the docs repo
it had been broken up into several discrete documents.  Now
that we've synced down the docs from that repo, our README
was redundant.  This commit replaces it with basically a
table of contents with links to the rest of the documentation.

This commit also removes CHANGELOG.md, which was duplicated by
`documentation/release_notes.markdown`, and FAQ.md, which is
replaced by `documentation/puppetdb-faq.markdown`.
Fix broken link to install docs
Merge pull request #414 from cprice-puppet/maint/master/puppetdb_docs-there_can_be_only_one

Maint/master/puppetdb docs there can be only one