Breaking change detection

[xuorig]

Currently anicca only computes differences but has no opinion on whether these changes are safe to make or not. We could add a breaking method on diff objects to solve that.

Then there's also some philosophical questions about whether a change is breaking or not. A change could be breaking to tools consuming OpenAPI, but not necessarily to the runtime of an API represented by this OpenAPI document. Do we differ between the two? Pick one?

[gr2m]

I think I'd leave breaking change detection to a secondary tool which can work with the output of anicca. That way folks can implement their own rules of what changes are handled as breaking changes and what others are not