Add Jaccard, Certainty, and Kulczynski association rules metrics

[UltraArceus3]

Description

We have implemented three association rules metrics: Jaccard Coefficient, Certainty Factor, and Kulczynski.
We have added appropriate test cases for each of these metrics.
We have also added an optional parameter to association_rules, called return_metrics. The user can pass in a list of metrics for the function to return, rather than having the function generate every implemented metric.

Related issues or pull requests

Resolves #1096

Pull Request Checklist

• Added a note about the modification or contribution to the ./docs/sources/CHANGELOG.md file (if applicable)
• Added appropriate unit test functions in the ./mlxtend/*/tests directories (if applicable)
• Modify documentation in the corresponding Jupyter Notebook under mlxtend/docs/sources/ (if applicable)
• Ran PYTHONPATH='.' pytest ./mlxtend -sv and make sure that all unit tests pass (for small modifications, it might be sufficient to only run the specific test file, e.g., PYTHONPATH='.' pytest ./mlxtend/classifier/tests/test_stacking_cv_classifier.py -sv)
• Checked for style issues by running flake8 ./mlxtend

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[UltraArceus3]

Hi @rasbt, we're looking at the failed formatting test case. The suggested formatting seems to be strange.

It looks like it is taking issue with two lines in test_association_rules.py. It is formatting just those two lines rather than the entire block. We could go back and change all the lines to reflect that same format, but then it would take up ~100 lines of just numbers. What are your thoughts?

[rasbt]

Code-wise, this looks pretty good to me!

[rasbt]

It looks like it is taking issue with two lines in test_association_rules.py. It is formatting just those two lines rather than the entire block. We could go back and change all the lines to reflect that same format, but then it would take up ~100 lines of just numbers. What are your thoughts?

Thanks for the PR. I am totally fine with not changing the formatting as suggested by black here. Let's see if this can be achieved via an # fmt: off

[rasbt]

Made the small formatting modifications! Thanks again for the PR, looks really good!

[Nachiket18]

Thanks @rasbt for reviewing and approving the change. It was fun to contribute to the library!

[ankithn30]

Thanks @rasbt for approving and reviewing our change! It was a great experience to contribute to this library!

[UltraArceus3]

Thank you @rasbt! It was great working with you on this change. We hope to continue contributing to your library in the future!