switch to github actions

[davidkoski]

@madrob when you get a chance can you please enable actions on this repository?

This sets up GitHub actions and is meant for post #441 -- it doesn't run the unit tests that were part of that split out.

I will either remove the .circleci change from 441 or need to handle the conflict here (trivial either way)

[madrob]

@davidkoski actions are enabled now, you might have to close and re-open the PR to get them to run the first time.

[madrob]

I think it's safe to delete the .circleci directory in this PR rather than waiting for the next one