public static ResponseTransformerRouteImpl create(String path,
                                                      String acceptType,
                                                      Route route,
                                                      ResponseTransformer transformer) {
        return new ResponseTransformerRouteImpl(path, acceptType, route) {
            @Override
            public Object render(Object model) throws Exception {
                return transformer.render(model);
            }

            @Override
            public Object handle(Request request, Response response) throws Exception {
                return route.handle(request, response);
            }
        };
    }
A ResponseTransformerRouteImpl is built up by a path (for url-matching) and the
implementation of the 'render' method. ResponseTransformerRoute instead of
returning the result of calling toString() as body, it returns the result of
calling render method.
The primary purpose of this kind of Route is provide a way to create generic
and reusable transformers. For example to convert an Object to JSON format.

@author alex
src/main/java/spark/ResponseTransformerRouteImpl.java