logger.go
func (l *Logger) Fatal(args ...interface{}) {
	l.log(CRITICAL, nil, args...)
	os.Exit(1)
}
func (l *Logger) Fatal(args ...interface{}) {
	l.log(CRITICAL, nil, args...)
	os.Exit(1)
}
// Fatal is equivalent to l.Critical(fmt.Sprint()) followed by a call to os.Exit(1).