gtk/print.go
func (ps *PageSetup) SetTopMargin(margin float64, unit Unit) {
	C.gtk_page_setup_set_top_margin(ps.native(), C.gdouble(margin), C.GtkUnit(unit))
}
func (ps *PageSetup) SetTopMargin(margin float64, unit Unit) {
	C.gtk_page_setup_set_top_margin(ps.native(), C.gdouble(margin), C.GtkUnit(unit))
}
// SetTopMargin() is a wrapper around gtk_page_setup_set_top_margin().