def set( index , value)
      raise "Only positive indexes #{index}" if index < 0
      if index >= get_length
        grow_to(index + 1)
      end
      if index >= data_length
        ensure_next
        next_list.set( index - data_length , value)
      else
        set_internal_word( index + self.class.type_length, value)
      end
    end
def set( index , value)
      raise "Only positive indexes #{index}" if index < 0
      if index >= get_length
        grow_to(index + 1)
      end
      if index >= data_length
        ensure_next
        next_list.set( index - data_length , value)
      else
        set_internal_word( index + self.class.type_length, value)
      end
    end
set the value at index.
 Lists start from index 0