Fixed status code errors by calling _process_options

Needed to use the `_process_options` method explicitly because the overriding of `render_to_body` in the `ControllerAdditions` module removes it from the call chain.

Should resolve https://github.com/apotonick/roar-rails/issues/71
Where is `_process_options` called in the original Rails code? Would it make sense to restructure the roar-rails responder to better fit into the original responder architecture (e.g. not overriding `#render_to_body` but something "smaller"?)? I am not that into responders, that's why I appreciate any kind of help here.