[Feature request] Calling neogen twice should overwrite the exising docstring

[theairbend3r]

The current behaviour is to add the docstring twice:

def my_func(a:int, b:str) -> str:
      """
   
      Parameters
      ----------
      a : int
          
      b : str
          
  
      Returns
      -------
      str
          
      """
      """
   
      Parameters
      ----------
      a : int
          
      b : str
          
  
      Returns
      -------
      str
          
      """
      return a * b

Overwriting the previous docstring would be more intuitive imo.

For example, if I change my function annotation and want to regenerate the docstrings, I'd rather have it overwrite the existing docstring instead of writing a new one below it.

What do you think?

[theairbend3r]

Discussion in #65.