Adding hypothesis as a dependency - #25

I will defer to @astrofrog as I wasn't very active in the relevant discussions in the POC PR.

cc @aarchiba and @Zac-HD

Will there be a release?

At some point yes. Do we need that now?

I'll let @aarchiba comment. I thought she said she needed this for her hypothesis PR in astropy.

🎉

Small question about versioning - does pytest-astropy really support Python 2.7, 3.3, and 3.4? Because the classifiers suggest it does, but Hypothesis only supports those versions supported by the PSF - i.e. 3.5+ from 2020-01-01. The classifiers also don't mention support for 3.7 and 3.8, though this is implied by the python_requires.

With my pytest maintainer hat on, 3.1 is quite badly out of date - 4.6 is the oldest currently-supported version, and that's a LTS branch we're keeping until the end of Python 2 support at the new year.

Suggestions:

• Add the 'Framework :: Hypothesis' classifier
• Specify a minimum Hypothesis version of 'hypothesis>=4.53', and consider bumping this to >=5.0 in early January (so that users can't start using deprecated features)
• Consider bumping the minimum Pytest version to 'pytest>=4.6'
• Ensure the Programming Language classifiers are up to date.
• If pytest-astropy is 3.5+, like astropy itself, bump the python_requires.

Thanks, @Zac-HD ! Please see #27

pytest-astropy was independent of astropy, so I believe supports for those versions of python were not untrue. However I think it's reasonable to clean up and drop a few versions now.

@astrofrog - what do you think?