Added all the callbacks to Window and GameState, removed all but one usage of global variables ().

lib/cyberarm_engine/opengl/renderer/renderer.rb

@@ -4,7 +4,7 @@ module CyberarmEngine
 
     def initialize
       @bounding_box_renderer = BoundingBoxRenderer.new
-      @opengl_renderer = OpenGLRenderer.new(width: $window.width, height: $window.height)
+      @opengl_renderer = OpenGLRenderer.new(width: CyberarmEngine::Window.instance.width, height: CyberarmEngine::Window.instance.height)
     end
 
     def draw(camera, lights, entities)