logging.go
func (logger *Logger) Errorf(format string, a ...interface{}) {
	logger.log(ERROR, format, a...)
}
func (logger *Logger) Errorf(format string, a ...interface{}) {
	logger.log(ERROR, format, a...)
}
func ( logger * Logger ) Errorf ( format string , a ... interface { } ) { logger . log ( ERROR , format , a ... ) }
// Errorf logs provided message with formatting in ERROR level.
Errorf logs provided message with formatting in ERROR level .