JavaDoc for TestedOn and ParametersSuppliedBy

Some simple javadoc for TestedOn and ParametersSuppliedBy, with mini examples, since I noticed they're still undocumented. There's a few other bits without much on them either that I'll get on soon too, this is just a start.

On a slightly-related note: is there a good reason why TestedOn only works for int parameters? Is there any appetite for opening this up just allowing any Objects to be specified? (especially since we now do autoboxing right, so Integer params would still work properly, and it'd be all nicely backward compatible)