message.go
func ParseMessageID(s string) (id MessageID, err error) {
	var v uint64
	v, err = strconv.ParseUint(s, 16, 64)
	id = MessageID(v)
	return
}
func ParseMessageID(s string) (id MessageID, err error) {
	var v uint64
	v, err = strconv.ParseUint(s, 16, 64)
	id = MessageID(v)
	return
}
// ParseMessageID attempts to parse s, which should be an hexadecimal
// representation of an 8 byte message ID.