Update to 4.13
    
    - New upstream release 4.13
      - For JSON_TYPE_INT and JSON_TYPE_FLOAT, allow to encode numeric values above
        2^64 in PV slot via Math::BigInt/Float (GH#145, GH#148, GH#149)
      - For JSON_TYPE_INT and JSON_TYPE_FLOAT encoder, allow to pass Math::BigInt
        and Math::BigFloat objects with allow_bignum (GH#147)
      - Fix encoding floating point values above 2^64 in PV slot to JSON_TYPE_INT
        (GH#148, GH#150)
      - Do not allow serializing objects when convert_blessed is not enabled
        (GH#146)