func NewGroup() *Group {
	in := make(chan Message)
	close := make(chan bool)
	return &Group{in: in, close: close, clock: 0}
}
func NewGroup() *Group {
	in := make(chan Message)
	close := make(chan bool)
	return &Group{in: in, close: close, clock: 0}
}
// NewGroup creates a new broadcast group.