Topic/dayssincereducer

Adds a day's since reducer, as well as a set of interval statistics reducers.
> Oh noes, do we use truthy/falsey stuff in Scala?

Definitely not. I was asking about `===`, which in scalaz is "type safe" equality, but in specs2 it's just a matcher (and `====` is the type-safe matcher). I was curious where the boolean was coming from.