Pass keywords from `pipes_dict` to `add_argument`

Objective
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 - create a tunnel to pass keywords into argparse from each dp.pipes ( #118 )
 - make easy to show parameters using `show_runs` pipe

Summary
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 - introduce "spec" (abbrev of special) keyword in `pipes_dict`
 - it will be troublesome to rewrite "args" or "kwds" definitions

Technical details
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 - remove `show` function from show.py, since `show_run` and `show_project` do not share codes.

PR status
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- blocked by #117 
- will resolve #118
- related to #109