@configure()

This is a change to config_changes that provides per-class `config` and keeps track of resourceConstructor via the new `configure` method, which applies new settings to the current config. The change is necessary because the previous version used the same `config` object for each class (new test would break). 

This allows for:

    class Book extends railsResourceFactory()
      @configure name: 'book', url: '/books'

    class CarManual extends Book
      @configure name: 'car_manual' 

When extending this way, at least one `@configure()` call is required.