code: func newLogger(tty bool, file string, verbose bool) log15.Logger {
  	stdoutFormat := log15.LogfmtFormat()
  	if tty {
  		stdoutFormat = log15.TerminalFormat()
  	}
  	stdoutHandler := log15.StreamHandler(os.Stdout, stdoutFormat)
  	if !verbose {
  		stdoutHandler = log15.LvlFilterHandler(log15.LvlInfo, stdoutHandler)
  	}
  	log := log15.New()
  	log.SetHandler(log15.MultiHandler(
  		log15.Must.FileHandler(file, log15.LogfmtFormat()),
  		stdoutHandler,
  	))
  	return log
  }
docs: // newLogger returns a log15.Logger which writes to stdout and a log file