Implement some kind of continuous integration

To run all tests periodically or when someone pushes stuff to the master branch.

Important to cover, imho:
- cloning of the repo into a fresh environment, setup the development environment, and run all tests.
- installation of the tool in an empty environment, run all tool tests, and run some more command line tests.

Inspect the repository's development setup and test commands first, then determine how to run them from a fresh clone and after installing the tool in an empty environment. Done means continuous integration runs on pushes to master or periodically, covers all tests, includes tool tests, and exercises command-line tests.

Written by the indexing model from the issue text.