title: generate python docstring template using current argument list
body: <p>I have a python package to release soon, so now I begin to slowly add docstrings to the files using vim. So for a func like</p>
  
  <pre><code>def foo(x, y, z=None, **kwargs):
  </code></pre>
  
  <p>I have to manually type the following repetitively for a whole day</p>
  
  <pre><code>""" foo does this stuff.
  
  Parameters
  ----------
  x: 
  y:
  z: optional
  kwargs:
  
  Returns
  -------
  
  """
  </code></pre>
  
  <p>Is there a way to dynamically generate this template docstring by defining some vim macros (which I know nothing of, so a suggestion for how to start would be great as well). Thanks.</p>