code: func (v *Container) ChildNotify(child IWidget, childProperty string) {
  	cstr := C.CString(childProperty)
  	defer C.free(unsafe.Pointer(cstr))
  	C.gtk_container_child_notify(v.native(), child.toWidget(),
  		(*C.gchar)(cstr))
  }
docs: // TODO: gtk_container_child_get_valist
  // TODO: gtk_container_child_set_valist
  // ChildNotify is a wrapper around gtk_container_child_notify().