Method add_option

plugins/manipulator.cpp:478–481

    }
    StringFormatter() {}
    void add_option(string spec, string help, string (*callback)(T))
    {
        opt_list.push_back(std::make_tuple(spec, help, callback));
    }
    T_optlist *get_options() { return &opt_list; }
    void clear_options()
    {