Hold finder's attribute per instance, instead of per class
Results can be displayed in bottom-up fashion (closes #9)

An option `--result-bottom-up` makes two changes:

  (1) display results bottom-up fashion, and
  (2) reverse line movement command behavior.

Another option `--prompt-bottom` let percol to display the prompt
bottom of the screen.
Command line option's document should be begun with a small-case letter.
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