logging.go
func (logger *Logger) AddHandler(handler Handler) {
	logger.lock.Lock()
	logger.Handlers = append(logger.Handlers, handler)
	logger.flushBuffer()
	logger.lock.Unlock()
}
func (logger *Logger) AddHandler(handler Handler) {
	logger.lock.Lock()
	logger.Handlers = append(logger.Handlers, handler)
	logger.flushBuffer()
	logger.lock.Unlock()
}
// AddHandler add new handler to current logger.