def reset
      output.each do |file, format|
        if File.exist?(file)
          utime(0,0,file)
          report "Marked #{file} as out-of-date."
        end
      end
    end
def reset
      output.each do |file, format|
        if File.exist?(file)
          utime(0,0,file)
          report "Marked #{file} as out-of-date."
        end
      end
    end
Reset output files, marking them as out-of-date.

 @return [void]