e2e-test-runner

A runner for Cara E2E tests (see the end-to-end-tests directory in the cara-lang/compiler repo).

The expected structure of these tests is:

- tests_root
  - first_test
    - main.cara
    - stdout.txt
  - second_test
    - main.cara
    - stderr.txt

etc.

• If stdout.txt is present, it is required for the actual stdout to match it.

• If it's missing, no stdout is allowed.

• If stderr.txt is present, it is required for the actual stderr to match it.

• If it's missing, no stderr is allowed.