Platform support policy proposal

There is a fair amount of confusion about the specific operating system platforms, platform versions, etc. that Chef Software, Inc. supports for its products. This RFC will clarify this by calling out the individual operating systems and their releases as explicitly supported or not.
I'll remove any language about CVT / omnibus testers as that's an implementation detail. Maybe I'll say something like a smoke test failure/integration test failure on a Tier 1 platform would be considered a blocker.