Port test.check/double

[steos]

Since the initial port test.check has gained a generator for floating point values. It would be great to have this available in PHPQuickCheck as well.

See
https://github.com/clojure/test.check/blob/000000076395383d824ec8a468a88ee2baa6f121/src/main/clojure/clojure/test/check/generators.cljc#L1069