Method on_string

test/basic_parser.cpp:1525–1525

            bool on_key( string_view, std::size_t, system::error_code& ) { return true; }
            bool on_string_part( string_view, std::size_t, system::error_code& ) { return true; }
            bool on_string( string_view, std::size_t, system::error_code& ) { return true; }
            bool on_number_part( string_view sv, system::error_code&)
            {
                captured.append(sv.data(), sv.size());