feat: Add function to find API breaking changes

[pawamoy]

Co-authored-by: Talley Lambert talley.lambert@gmail.com

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@tlambert03, following discussion in #75, I've taken your code in griffediff, updated it to my taste (I hope you don't mind 😓) and credited you of course. This PR is still a draft anyway, just experimenting a bit.

What I envision is:

• utility to yield more than breakages: yield everything that changed or was added/removed (for auto-documentation purposes) and attach these data to objects
• also attach detected breakages to objects
• utility to yield forward-compatibility hints: "set these parameters as keyword-only" here and there, etc., and attach these data to objects. These hints could be displayed in docs auto-generated through mkdocstrings when serving only, to inform the developer 🤔
• of course: add CLI options to show hints and breakages

[tlambert03]

nice! looking good! :)