Some improvements

[friefi]

I would like to suggest some improvements to the argparse project:

• introduction of count limits for multi-value args
• providing result collections for parse errors instead of writing to cerr
• modifying the validate() method to not exit the program and validate "unknown" args as well
• fixing issue when a value of a multi-value arg contains commas

I would go ahead and do a pull request, if appreciated.

[morrisfranken]

Hi Friefi, thanks for the suggestions, this is much appreciated.

I'd be happy to accept the pull request for these points. And as for the count limits, what would be the use case for this?

Looking forward to the pull request!