0.01_05
    refactoring encode_attrs
    refactoring decode_attrs

0.01_04
    delete cycle_attrs no_ret option 

0.01_03
    add cycle_attrs

0.01_03
    add clone method
    add freeze method
    add thaw method

0.01_02
    add encode_attrs method
    add decode_attrs method

0.01_01
    First developer release