func Fatal(format string, v ...interface{}) {
	FatalDepth(4, format, v...)
}
Fatal writes formatted log in Fatal level then exits.
package clog
import (
	"fmt"
	"os"
)
type Level int
const (
	LevelTrace Level = iota
	LevelInfo
	LevelWarn
	LevelError
	LevelFatal
)
func (l Level) String() string {
	switch l {
	case LevelTrace:
		return "TRACE"
	case LevelInfo:
		return "INFO"
	case LevelWarn:
		return "WARN"
	case LevelError:
		return "ERROR"
	case LevelFatal:
		return "FATAL"
	default:
		fmt.Printf("Unexpected Level value: %v\n", int(l))
		panic("unreachable")
	}
}
func Trace(format string, v ...interface{}) {
	mgr.write(LevelTrace, 0, format, v...)
}
func Info(format string, v ...interface{}) {
	mgr.write(LevelInfo, 0, format, v...)
}
func Warn(format string, v ...interface{}) {
	mgr.write(LevelWarn, 0, format, v...)
}
func Error(format string, v ...interface{}) {
	ErrorDepth(4, format, v...)
}
func ErrorDepth(skip int, format string, v ...interface{}) {
	mgr.write(LevelError, skip, format, v...)
}