Remove extra whitespace in PubSub
Add tests suite; add PubSub listener inversion

lib.PubSub now has two additional methods inspired by the Backbone
events API - `#listenTo` and `#stopListening`. All listeners created
by `listenTo` will be removed all at once when `stopListening` is
called. Being able to remove all the listeners in this fashion makes
listener leaks easy to avoid when repeatedly constructing/deconstructing
objects.

There are tests for these new methods in a folder called `tests`. The
method interfaces are documented with JSDoc style comments within
PubSub.js.
Merge pull request #68 from gameclosure/feature-pubsub-listener-inversion

Feature pubsub listener inversion