Update 2.2.3 with new tests; move some old ones to 2.1.2.

This is a consequence of promises-aplus/promises-spec@9ba58eb04e2b17bda7c078459651bd7b79ec6d6f.
Add extensive tests for the new 2.2.4.

This is a consequence of promises-aplus/promises-spec@f35ef373a45746a17a156ddc50e02e9e3702ceeb.
Add sneaky test for 2.3.3.3.3, kudos @stefanpenner.

Closes #38.