Set up tox tests with coverage

[wlonk]

I want 100% coverage.

[wlonk]

And pytest.

[josheppinette]

https://github.com/jteppinette/python-logfmter

I recommend checking out my actively maintained python-logfmter package.

We have tox integration and a full test suite.

[wlonk]

Love it, thank you!