title: Verbose level with argparse and multiple -v options
body: <p>I'd like to be able to specify different verbose level, by adding more -v options to the command line. For example:</p>
  
  <pre><code>$ myprogram.py    
  $ myprogram.py -v
  $ myprogram.py -vv
  $ myprogram.py -v -v -v
  </code></pre>
  
  <p>would lead to verbose=0, verbose=1, verbose=2, and verbose=3 respectively. How can I achieve that using argparse?</p>
  
  <p>Optionally, it could be great to also be able to specify it like</p>
  
  <pre><code>$ myprogram -v 2
  </code></pre>