code: func NewPingChecker(ip net.IP) *PingChecker {
  	proto := seesaw.IPProtoICMP
  	if ip.To4() == nil {
  		proto = seesaw.IPProtoICMPv6
  	}
  	id := nextPingCheckerID
  	nextPingCheckerID++
  	return &PingChecker{
  		Target: Target{
  			IP:    ip,
  			Proto: proto,
  		},
  		ID: id,
  	}
  }
docs: // NewPingChecker returns an initialised PingChecker.