Method emplace

include/jsoncons/json_array.hpp:207–211

        template <typename A=allocator_type,typename... Args>
        typename std::enable_if<std::allocator_traits<A>::is_always_equal::value,iterator>::type 
        emplace(const_iterator pos, Args&&... args)
        {
            return elements_.emplace(pos, std::forward<Args>(args)...);
        }

        template <typename... Args>
        Json& emplace_back(Args&&... args)