Adapt Python generator to Roc

[ageron]

I copied Python's bin/generate_tests.py script and its dependencies (bin/data.py, config/generator_macros.j2, and requirements-generator.txt), and I adapted it to Roc.

To use:

• Create a .meta/template.j2 file.
• Run bin/generate_tests.py

This will generate the <slug>-test.roc file for each exercise. See bin/generate_tests.py --help for more options.

I also added a template.j2 file for the two existing exercises (hello-world and leap) and regenerated the test scripts.

Now that we have a roc-test-runner and generator script, and a couple working exercises, we can start adding new exercises quickly! 😊

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

For more information, refer to the documentation. If you are unsure whether to add the message or not, please ping @exercism/maintainers-admin in a comment. Thank you!

[ErikSchierboom]

Great idea

[ageron]

Thanks Erik ☺️