title: argparse for unknown number of arguments and unknown names
body: <p>I'd like to fetch all parameters passed to <code>sys.argv</code> that have the format<br>
  <code>someprogram.py --someparameter 23 -p 42 -anotherparam somevalue</code>.</p>
  
  <p>Result I'm looking for is a  namespace containing all the variables, already parsed.</p>
  
  <p>To my understanding, argparse is expecting the user to define what are the parameters he is expecting.</p>
  
  <p>Any way to do that with argparse ?
  Thanks ! </p>