reducing the amount of written code for helpers that delegate methods to other objects

[erisdev]

I've made use of Ruby's Forwardable module to shorten delegate methods to a single line each. Thus:

def add_game_object(object)
  @game_objects.add_game_object(object)
end

becomes

def_delegator :@game_objects, :add_game_object

Also extracted the duplicated FPS counter code from Window and Console into a new helper module.