Add exoskeleton todomvc.

[Exoskeleton](http://exosjs.com) is a faster and leaner Backbone.

No deps on jQ or underscore here. This required modified BB.localstorage — I have submitted a PR to it which removes underscore dep.

I will add the readme in a bit.

as [asked](https://twitter.com/addyosmani/status/393880686504865792) — cc @addyosmani @sindresorhus