WIP: PuppetDB 1.1 docs

So far these commits just attempt to sync up the latest changes from the README.md in the puppetdb repo.  There is still stuff to do before this gets merged, but I just wanted to get it up so that docs team could start looking at it.

Known outstanding issues / work:

* Probably need to improve `install_via_module.markdown`
* Need to sync up changes from the `documentation` directory in the puppetdb repo, including directory reorganization, versioned HTTP endpoints, etc.