Hi all, I've created a PR for this, please help for code review.

I found that previous method from Oz had a problem, that man page and general help page will share a Formatter, that cause an unexpected behavior that help page will generate with troff format (Unix man page used this format).

I switch to another method that creates a Manpage class and a private _ManpageFormatter, we just need to put parser into this Manpage, the __str__ method will generate the man page that we want.

This approach prevents help page format affect by ManpageFormatter, and the user can happily switching formatter_class to RawDescriptionHelpForatter, RawTextHelpForatter and others, since the Manpage class is separate from HelpFormatter, and _ManpageFormatter will used the formatter provide from parser.

The attach file is a dummy argparser file, you can try it by this:

  ./python poc.py > poc.1 && man ./poc.1