Make Clone a supertrait of Shrink.
Basic quickcheck appears to work.
Merged Arbitrary and Shrink traits.
Consistent doco.
Add doco. Add prime number sieve test. Add attempt to catch runtime
errors. (Couldn't get it to work.)
Lots more to say in the README. Add examples.
The sieve test should fail.
remove debugging junk
Update to work with relocation of rand crate.