Pystow

What's Changed
* Ensure API completeness by cthoyt in https://github.com/cthoyt/pystow/pull/29
* Fully document pystow and pass darglint checks by cthoyt in https://github.com/cthoyt/pystow/pull/33
* Fix 31 by dobraczka in https://github.com/cthoyt/pystow/pull/32
* More typing and testing by cthoyt in https://github.com/cthoyt/pystow/pull/34


**Full Changelog**: https://github.com/cthoyt/pystow/compare/v0.3.0...v0.3.1

What's Changed
* Fix minor typo in ensure_json example by dobraczka in https://github.com/cthoyt/pystow/pull/25
* Document ensure_open_zip by dobraczka in https://github.com/cthoyt/pystow/pull/27
* Drop legacy py36 and update CI by cthoyt in https://github.com/cthoyt/pystow/pull/30
* Add numpy I/O by cthoyt in https://github.com/cthoyt/pystow/pull/28


**Full Changelog**: https://github.com/cthoyt/pystow/compare/v0.2.8...v0.3.0

- Improve documentation for ensuring RDF ( 24, thanks dobraczka)
- Fix sphinx documentation of `pystow.utils` submodule

- pin old flake8 version in CI since new one is broken
- update docs
- add mocks for tests
- add new opener functions (they don't have top level functions yet)

- Blacken all code
- Remove deprecated get() function
- Add ensure_json() function that works similarly to ensure_csv() and other ensure_functions(). One thing it doesn't do is canonicalize the JSON, which is sometimes annoying

- Refactor hex digest generation
- Fix bug in type casting from env