Add gen/uniform-double

Question

Would be somewhat of a utility generator -- generates a double from 0.0 (inclusive) to 1.0 (exclusive), and doesn't shrink.

{{gen/choose}} could even be rewritten with {{gen-fmap}} if we had this.

Answer 1

Reference: https://clojure.atlassian.net/browse/TCHECK-84 (reported by gfredericks)