title: argparse add_argument alias
body: <p>Is there a way to create an alias using argparse?</p>
  
  <p>For example, I want to do something like this:</p>
  
  <pre><code>parser.add_argument('--foo' ...)
  parser.add_argument_alias('--bar', '--foo')
  </code></pre>
  
  <p>That is, using <code>--bar</code> should be equivalent to using <code>--foo</code>.</p>