Add a simple test runner for basilisp.test

[mitch-kyle]

It would be nice to be able to run tests in the repl with the basilisp.test namespace.

The proposed changes:

• Add run-tests, and run-all-tests, etc as in clojure.test to basilisp.test.
• Add a mechanism to basilisp.test for applying test fixtures. This is useful for building tests in the repl.

These would be nice to have but not necessary:

• cider-test / nrepl integration