func SetLevel(lvl int) {
	switch lvl {
	case LevelAll, LevelDebug, LevelInfo, LevelWarn, LevelError, LevelNone:
		DefaultLogger.SetLevel(lvl)
		break
	default:
		fmt.Fprintf(Output, "invalid log level: %v", lvl)
	}
}
SetLevel sets default logger's priority.
package log
import (
	"fmt"
	"io"
	"os"
	"time"
)
var (
	TimeFormat = "2006/01/02 15:04:05.000"
	Output io.Writer = os.Stdout
	DefaultLogger Logger = &logger{level: LevelInfo}
)
const (
	LevelAll = iota
	LevelDebug
	LevelInfo
	LevelWarn
	LevelError
	LevelNone
)
type Logger interface {
	SetLevel(lvl int)
	Debug(format string, v ...interface{})
	Info(format string, v ...interface{})
	Warn(format string, v ...interface{})
	Error(format string, v ...interface{})
}
func SetLogger(l Logger) {
	DefaultLogger = l
}