Operators couldn't return boost::python::object

When I trying to define operator which returns boost::python::object I get error ` ‘struct boost::python::converter::arg_to_python’ has no member named ‘release’`

`def` method for operators doesn't accept additional arguments to define other converters.

首先重現一個回傳 boost::python::object 的運算子，並追蹤提及 arg_to_python 和 release 的轉換器錯誤。調查 def 方法如何處理運算子轉換器；當此類運算子能夠運作並接受必要的轉換器引數時即可完成。

由索引模型根據 Issue 內容生成。