Make Chance conform to Comparable

[Samasaur1]

The Chance type should be Comparable. It definitely should be comparable to itself, probably to Doubles, and possibly even to Ints (allowing one to say myChance > 0).

[Samasaur1]

30c71fc starts to address this

[Samasaur1]

It makes Chance comparable to itself, and also to integers. It doesn't make it comparable to Double (or Float, I guess) because I wasn't sure whether to compare Chance.value with the double, or Chance(approximating:) with the chance.