Add CI integration

[tatablack]

Once we have a test suite, we may want to run it at every change.

CircleCI:

https://circleci.com/docs/2.0/first-steps/

GitHub Actions

https://help.github.com/en/actions/automating-your-workflow-with-github-actions/starting-with-preconfigured-workflow-templates

https://github.com/marketplace

https://github.com/tatablack/leaner-coffee-powerup/actions/new