Allow arbitrary overriding of comparision methods

[z33ky]

subclasses should be allowed to override these with differing argument types.

The documentation explicitly allows returning non-bool values for instance.

This also allows typeshed to define comparison methods for object and still error on comparisons of unrelated types (like str() < int()).

[gvanrossum]

This PR is missing tests for the new functionality. But first I would like to see an issue filed requesting this change -- I would like to see some specific use cases to decide what to do here, and completely excluding the comparisons from compatibility with the base class feels wrong (they are not as unrelated as __init__ or __new__).

[JukkaL]

Agreed that this would benefit from discussion.

[gvanrossum]

Closing this PR, let's continue the discussion in #2661.