def custom_reader(key)
      default_proc.call(self, key) if default_proc && !key?(key)
      value = regular_reader(convert_key(key))
      yield value if block_given?
      value
    end
def custom_reader(key)
      default_proc.call(self, key) if default_proc && !key?(key)
      value = regular_reader(convert_key(key))
      yield value if block_given?
      value
    end
Retrieves an attribute set in the Mash. Will convert
 any key passed in to a string before retrieving.