Extend Q_PROPERTY with more keywords...

It would be nice with more keywords (attributes) for Q_PROPERTY, e.g:

TOOLTIP <string> : a tooltip for the property, so that when the property is in a property tree widget, the tooltip can be displayed to it
DELEGATE <fn> : a function returning a delegate, to aid in editing the property
HELP <fn> : a function called if user presses F1 (help) when editing
USER <void*> : a user-defined value

At least the USER attribute should be added to make it possible to extend the property system.