Add basic autotests setup

[m-hurlow]

This integrates the autotests library into new Python eval functions by default, allowing documentation examples to be automatically built from integration tests.

Changes:

• Added a dependency on autotests in requirements.txt.
• Added an empty eval_tests.yaml.
• Put the auto_test decorator on the class in evaluation_tests.py so that any tests in eval_tests.yaml will be run.
• Made a note in the README that eval_tests.yaml should be updated with tests as the function is developed.

[m-hurlow]

P.S. I also think that this repo should be migrated to use the new eval function architecture based on Shimmy (hence the review from Andreas). I don't have the time to do this now, so maybe this could be considered later.