Fixes and browserify init change

This commit includes @domenic's [changes](https://github.com/shtylman/zuul/pull/11), fixes/re-arranges some things and changes one part of the `config` API.

`exports.browserify` is now `exports.initBrowserify(browserify)` for the following reasons:
- ensure same browserify version
- implementer no longer has to depend on browserify
- its more consistent with `initApp`