Initial endless runner work.
More work.
Merge.
Remove comment.
Animation changes.
Merge branch 'master' into runner
Fix jumping by not mutating vector in-place. Should be fixed in vector model
Coin emitter.
Remove old asset.
Make coin movement wary of world speed.
Adjust gravity vector.
refinments, GLOBALS, end screen.
Minor refinements. Maybe a title screen?
much numbers, time left.
Add bundled game so we  don't have to  compile when shared.
quick hack to kill off black background. not perfect, but mostly works.
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.
Ensure we apply Sprite constructor with new inheritance model.