QCustomPlot Discussion and Comments

On Ubuntu 22.04, QT5 version is 5.15.3

I did this modification (generalized each time it is used) to avoid warning

#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
#if QT_VERSION >= QT_VERSION_CHECK(5, 13, 0)
result->setRenderHint(QPainter::Antialiasing);
#else
result->setRenderHint(QPainter::HighQualityAntialiasing);
#endif
#endif

Thanks for the feedback!
Will be fixed in the next revision.