Travis improvements

[JamesOwers]

I didn't have time to do everything I wanted for travis. Things to add:

• [ ] Make sure black, isort, and flake8 are run
• [ ] Test all the different install options
• [ ] Test but allow 3.8 and nightly to fail
• [ ] Test on macos and windows
• [x] codecov badges! done in #146

https://blog.travis-ci.com/2019-08-07-extensive-python-testing-on-travis-ci

Bigger stuff:

• [ ] integration test for data creation process #145