Method operator+

unittests/catch.hpp:6303–6303

        auto operator+=( T const &other ) -> Parser & { return operator|=( other ); }
        template<typename T>
        auto operator+( T const &other ) const -> Parser { return operator|( other ); }

        auto getHelpColumns() const -> std::vector<HelpColumns> {
            std::vector<HelpColumns> cols;