Added support for a :scoped parameter to indicate that controller URLs should be scoped

The :scoped parameter makes it easy to specify that controllers should be scoped when generating docs. For my use case I specify API versions in my routes via an accept header such as application/vnd.example.v1+json along with a route constraint. As such, controllers live in app/controllers/v1, app/controllers/v2, etc, but all api endpoints are scoped to the root URL. Adding :scoped => true allows for per version documentation consistent with the underlying API routes.