Evaluate API for `random(inRange:)`

[andrewdolce]

From a TODO in UnsignedInteger+Extensions: There is a public function random that takes in a CountableClosedRange of integers and returns a random int from within the range. The TODO comment suggests that this function could live as a member function on CountableClosedRange. So it would look something like:

(0..<10).ip_random()

I think to address this issue we need to:

1. Start a discussion about whether we like this idea.
2. Try switching the code to use the new API, with updated test coverage.

Not necessarily in that order. I think taking a stab at (2) could help inform (1).

[brightredchilli]

I say we go ahead and do it.

This interface ip_random(0..<10) seems very C-style and not swift-3 like.

Take:

dispatch_async(dispatch_get_main_queue(), ...)

vs

DispatchQueue.main.async( ... )

or any one of the map/reduce operators that have now gone on to be implemented in the collection extensions as opposed to being implemented as global functions. Happy to stand corrected on this though!