Respect upper-bound of `choose` during shrinking

Commit f2f23a21dc5c95664d44290c1b1c5db095566423 only addressed
respecting _lower_ bounds. This was fine if the upper bound was a
positive number, but when both the lower and upper bounds are negative,
like `(choose -50 -20)`, the generator would shrink to numbers greater
than `-20`. This commit also adds a test.
Fix/cleanup docstrings

A set of parens was missing, and another was indented funny.
Merge pull request #39 from fredericksgary/patch-2

Fix/cleanup docstrings
simple-check now Clojure/ClojureScript portable via cljx, fixes gh-11
Refactor `defspec` impl to avoid repeated re-defs in ClojureScript.

The prior approach was producing undefined function references in
:advanced-optimized JavaScript, perhaps due to fn references going
stale in the _ClojureScript_ compiler...?