Add support for CommonJS, AMD, and global namespace usage methods.

I want to use modules like [browserify](http://browserify.org/) with backbone-nested, but found I could not in its current state. This adjustment adds CommonJS, AMD, and keeps the global `window` namespace support.

Some things I'm curious about:

* Tests for this are possible, but I'm only familiar with mocha. The tests you have within QUnit seem to continue passing, though.
* Wonder if we can remove the jQuery dependency by finding a different method to `deepClone`?

I am fairly new to using CommonJS modules in the browser but the pattern I used below is the same one used by other backbone modules like [backbone.epoxy](https://github.com/gmac/backbone.epoxy/blob/master/backbone.epoxy.js)

Thanks for your time, and I hope this helps!