list.go
func NewList(w *Window, x, y int) (Widgeter, error) {
	return &List{
		Widget: MakeWidget(w, x, y),
	}, nil
}
func NewList(w *Window, x, y int) (Widgeter, error) {
	return &List{
		Widget: MakeWidget(w, x, y),
	}, nil
}
// NewList is the List initializer.  This call implements the NewWidget
// convention by taking a *Window and and an anchor point to render the widget.