The splitting of rendering and processing is good, but on the other side
it makes some double steps or even introduce workarounds.
That is why I made the method #render just a call to the renderer. This
should help much more than the strict seperation.
The method will only return the resulting string and not add it to the
body of the response. That still has to be taken care of by the user.
This avoids hardcoding the options into the controller and therefore
should it make possible to use Rack::Request or Sinatra apps as
requests. (That sounds so weird.)
