Method on_uint64

test/basic_parser.cpp:1537–1542

                return true;
            }
            bool on_uint64( std::uint64_t, string_view sv, system::error_code& )
            {
                captured.append(sv.data(), sv.size());
                captured += 'u';
                return true;
            }
            bool on_double( double, string_view sv, system::error_code& )
            {
                captured.append(sv.data(), sv.size());