Option.none_()

I've added a `none_()` method to `Option`, for parity with `some_()`.  I had a need for this in [my own code](https://bitbucket.org/alreadythere/porkbelly/src/69e4b3250979/src/main/java/com/mergeconflict/porkbelly/MatcherF.java), where depending on one's level of optimism, one can either declare a "matcher" that matches everything or nothing.