Setup pytest and flake8 to run in github actions

[jonathannaz]

I think the Travis CI code was using pytest to run the tests and flake8 for linting, any chance you'd be able to hook those up too? Looks like I had it hooked up to Codecov for coverage reporting, not sure if it's worthwhile trying to get that working but wondering if Github just has something that's super cheap/quick to set up?

from: #31 (comment)