func SetDefault(log Logger) {
	defLogger = log
}
SetDefault the default logger to be returned by
Default() and L(). This method is expected to
be called early in the program to setup a default
logger.
package log
import (
	"io"
	"os"
	"sync"
)
const DefaultTimeFormat = "2006-01-02T15:04:05.000Z07:00"
var (
	defLock   sync.Once
	defLogger Logger
	DefaultOutput io.Writer = os.Stderr
	DefaultLevel = Off
)
func Default() Logger {
	defLock.Do(func() {
		if defLogger == nil {
			defLogger = New(&LoggerOptions{
				Level:  DefaultLevel,
				Output: DefaultOutput,
			})
		}
	})
	return defLogger
}
func L() Logger {
	return Default()
}