More code API-level functional test coverage.

* Update async invocation of general validator functions in xtrudr.js
  to ensure that they are called after named validator functions, and
  in the order they are registered.

* Add test coverage for the rest of the defaultMsgs fns.

* Add async API tests.  While 100% coverage has been achieved, not all
  use cases are satisfactorily covered.
Add npm badge to README.  Configure travis for auto-deploy to node.