QPainterPath should have relative versions of moveTo, lineTo, arcTo, cubicTo and quadTo

The QPainterPath class currently provides the moveTo(), lineTo(), arcTo(), cubicTo() and quadTo() functions but these only take absolute coordinates. For relative coordinates, i.e. coordinates relative to currentPosition(), it would be useful to have relMoveTo(), relLineTo(), relArcTo(), relCubicTo() and relQuadTo(). For comparison see Cairo: http://www.cairographics.org/manual/cairo-Paths.html#cairo-rel-curve-to and following sections. (Note: Cairo currently doesn't have relArcTo and quadTo/relQuadTo.)

This would be a simple patch but would be very useful IMHO. I will see if I can whip up a patch.