Bitraversable laws

[sjakobi]

…would be nice to have.

https://hackage.haskell.org/package/base-4.16.1.0/docs/Data-Bitraversable.html#t:Bitraversable

[sjakobi]

Similarly to the Traversable laws, implementing the naturality law might be a bit tricky. Compare #24 (comment).