Support Fantasy Land's Setoid type (fantasy-land/equals method) in the matching algorithm.

[dead-claudia]

This is easy to integrate into the matching algorithm, and usually, these are more correct than a simple object match.

Also, include a fallback for literally a.equals(b), since that's available in even more libraries.

Note: I'll need to run the benchmarks for this again, because I don't want it to be too slow. (I need to revisit those, anyways.)