showdoc only shows first returned object for numpy docstrings

[nikolas-claussen]

For a function that returns multiple objects, parsing a numpy-style doctring with nbdev.showdoc (and nbdev_preview in the command window) only shows the first returned object. Example:

def f(x):
    """
   foo

    Parameters
    ----------
    x : int
    
    Returns
    -------
    a : int
    b : str

    """
    return a, b

This gives a docstring that only mentions "a" and not "b".