def last_file
      @last_file ||= begin
        # Preserve one prior version of the log file
        FileUtils.mv Log.log_file, "#{Log.log_file}.old" if File.exist?(Log.log_file)
        open_log(Log.log_file)
      end
    end
def last_file
      @last_file ||= begin
        # Preserve one prior version of the log file
        FileUtils.mv Log.log_file, "#{Log.log_file}.old" if File.exist?(Log.log_file)
        open_log(Log.log_file)
      end
    end
Returns a logger instance that will send to the log/last.txt file