Function utf16to8

external/utf8/cpp11.h:40–45

    }

    inline std::string utf16to8(const std::u16string& s)
    {
        std::string result;
        utf16to8(s.begin(), s.end(), std::back_inserter(result));
        return result;
    }

    inline std::u16string utf8to16(const std::string& s)
    {