def get_class_by_name!(name , super_class = :Object)
      c = get_class_by_name(name)
      return c if c
      create_class( name ,super_class)
    end
def get_class_by_name!(name , super_class = :Object)
      c = get_class_by_name(name)
      return c if c
      create_class( name ,super_class)
    end
get or create the class by the (symbol) name
 notice that this method of creating classes implies Object superclass