require.extensions deprecated, switch to browserify

not sure when it happened, but require.extensions (used to do the bones.js loading) has been deprecated for a while [see the docs](http://nodejs.org/docs/latest/api/globals.html#globals_require_extensions)

I've recently been doing a little demo project with [browserify](https://github.com/substack/node-browserify) and the [browserify-middleware](https://github.com/ForbesLindesay/browserify-middleware), and I managed to get a big chunk of that side of bones' functionality through just a few lines of code.

it's wonderful not having to have the separate backbone/jquery in assets anymore, and it makes upgrading those so much simpler. hell, the amount of code re-use just shoots through the roof.

when it comes time to upgrade my fork to 0.10.x/0.12.x, i will probably rewrite it to use browserify instead.