Add npm test.
Provide better functionality for inheritance using super from npm.

Scene/Entity can now be used ala Backbone extends:

var Player = Entity.extend({
    initialize: function(options) {
        // custom init logic.
    }
});

This keeps the core logic of the Entity and Scene out of harms way (unless
explicitly trying to change it), and gives a consitent method of
inheritance as we lacked that until this point.
Simple test for inheritance.