Add a way to compute the Leibniz formula.

[unibara]

-> https://en.wikipedia.org/wiki/Leibniz_formula_for_π

I have written an algorithm that calculates the Leibniz formula, which can be used to estimate the mathematical constant π.

Describe your change:

• [x] Add an algorithm?

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [x] All new Python files are placed inside an existing directory.
• [x] All filenames are in all lowercase characters with no spaces or dashes.
• [x] All functions and variable names follow Python naming conventions.
• [x] All function parameters and return values are annotated with Python type hints.
• [x] All functions have doctests that pass the automated testing.
• [x] All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.

[stale[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[cclauss]

In preparation for that denial-of-service attack that is Hacktoberfest, I am closing all pull requests that have failing tests.