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 
Hadoop already has counters for things like number of records read, number of reduce groups, number of reduce output records. I think for this app, creating a counter for number of renamed facts would be good. Not sure what else