Function assign_difference

include/chaiscript/dispatchkit/operators.hpp:48–51

      template<typename T>
        void assign_difference(Module& m)
        {
          m.add(chaiscript::fun([](T &lhs, const T&rhs)->T&{return lhs -= rhs;}), "-=");
        }

      template<typename T>
        void assign_left_shift(Module& m)