Improve formatting of Hypothesis example output

[DRMacIver]

This changes our printing logic to use the pretty printing library. This is partially to give nicer output, partially to give us a bit more control over how things are printed as setup for some later features...

While here I noted that the stateful testing library outputs a bunch of garbage from @given that is totally irrelevant to the user, and it was easier to fix that behaviour than fix the tests to assert the right things about its format, so I did that too.

[DRMacIver]

I think the coverage problem is pointing to something dark and terrible being wrong in Hypothesis's handling of positional arguments. 😢

[DRMacIver]

I'm going to need to park this for some investigation of what the hell is up with positional arguments in @given and I should really be marking linear algebra instead of working on this.

[DRMacIver]

I think the coverage problem is pointing to something dark and terrible being wrong in Hypothesis's handling of positional arguments. 😢

Fortunately this turns out not to be the case. I still think there's probably something dark and terrible in there but I choose to ignore it for now.

[Zac-HD]

I still think there's probably something dark and terrible in [handling of positional arguments] but I choose to ignore it for now.

Positional-only arguments, for example... but I'm also ignoring this until after the Py2/Hy5 transition. Or possibly #961 / #2231 😬