Express 4.x support

Initial drop for Express 4.x support. This includes:

* Allowing for the extension of Express 4.x Routers as well as Express 4.x apps
* Normalizing Express 4.x routes so that they return the same output as Express 3.x when calling `app.findAll()` or `router.findAll()`.

To do:

* Tests for Express 4.x Routers.