Added ability to rename features

I'm not completely satisfied with this, but wanted to get it open sooner rather than later. I'll leave a few inline comments. The branch obviously won't build until we do something with `IvoryT` (I really wish you could re-target PRs in GH)

/cc @etorreborre @markhibberd @raronson 
> I don't think the value is right here, it should be just a ThiftFact not a namespaced one. See comment in reducer.

You're right, I just hit this as I was switching over to renaming namespaces. I can see how the spec was wrong, but not sure how the cli test passed.