Set us up some CI

[dcreager]

We should set up some CI to run the test suite for each candidate PR.

(To be clear, we were doing this before! We should just start doing it again now that the library is open sourced.)

[gjedeer]

Since you're providing a Docker image too, perhaps the CI should also try docker building the image (since, as of now, it fails)

[patrickt]

Both of these issues should be fixed with #110.