window.go
func (w *Window) keyHandler(ev termbox.Event) (bool, Windower, Widgeter) {
	if w.focus < 0 || w.focus > len(w.widgets) {
		return false, w.mgr, nil // not used
	}
	return w.widgets[w.focus].KeyHandler(ev), w.mgr, w.widgets[w.focus]
}
func (w *Window) keyHandler(ev termbox.Event) (bool, Windower, Widgeter) {
	if w.focus < 0 || w.focus > len(w.widgets) {
		return false, w.mgr, nil // not used
	}
	return w.widgets[w.focus].KeyHandler(ev), w.mgr, w.widgets[w.focus]
}
// keyHandler routes event to proper widget.  This is called from queue context
// so be careful to not use blocking calls.