Reference: https://man.freebsd.org/cgi/man.cgi?query=md5sum
Add cli-tests to `make test`. This adds a `python3` dependency to `make test`, but not `make check`. We could make this dependency optional by skipping the tests if `python3` is not present.
Adds the new CLI testing platform that I'm proposing. See the added `README.md` for details.