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 
Are you storing the `date` twice here? once in `fact.date.int` and the other in `fact.datetime`. I don't think i have the full context, so probably missed something.