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 see how this works - the bytes here are set in the ValueState which is the "Namespaced" version rather than the raw fact - so isn't this writing out the wrong type of fact?