const RFC3339Milli = "2006-01-02T15:04:05.000Z07:00" // RFC3339 with 3 decimal places, padded
func SetOutput(logger *log.Logger, w io.Writer, format string)
Configure the logger to emit formatted timestamps to the given writer. The format string must always produce output that is no longer than the format string itself, otherwise behavior is undefined. If logger is nil, then the default logger is updated.