Function toLowerInPlace

tests/catch.hpp:11127–11129

        return s.find( infix ) != std::string::npos;
    }
    void toLowerInPlace( std::string& s ) {
        std::transform( s.begin(), s.end(), s.begin(), toLowerCh );
    }
    std::string toLower( std::string const& s ) {
        std::string lc = s;
        toLowerInPlace( lc );