Bootstrap Hedgehog

I think it would be a good idea to use the most recent stable version of Hedgehog to test the next/unstable version. Having property tests for Hedgehog itself would make the codebase much stronger (I realize we already use the current version for some tests), but I don't think using the unstable version to test itself is a good idea.

I'm also open to using another PBT library (FsCheck, etc) for this purpose, however I think it would be neat to use our own library.