Promote arbitrary ==>> to scalacheck-binding.
Test soundness (order preservation) of a few ==>> operations. (union fails)
Symmetricity and more idempotence tests.
More ==>> difference tests.
A failing ==>> intersection sample.
A sample of intersection failing.
a intersect a = a
partition soundness
fix scalaz.==>> bug
Fix variable references on ==>> split/filter/join; property-based ==>> tests. (#511)