Using shared_ptr in exception class

[OlegGalizin]

By
https://en.cppreference.com/w/cpp/error/exception
Each standard library class T that derives from std::exception has the following publicly accessible member functions, each of them do not exit with an exception(until C++11)having a non-throwing exception specification(since C++11): copy_constructor

For copy unique_ptr we must allocate new space and copy object into one. The allocation can throw exception. So we cannot use unique_ptr.

I change it to shared_ptr that works without memory allocation in copy constructor.