Factor out Exhibitor

This PR is a massive change to accommodate the new [Exhibitor cookbook](). It will be a full version bump to 2.0.0, but is now a pre-release. I'll test for the next day or two both this and Exhibitor (and clean up both), and I intend to make this a LWRP, probably maintaining a default recipe to keep backwards-compatibility.

Supercedes #76 
Ah, excellent. You can tell I use Berks and TK a lot eh? :)