Merge and format the docstring definition with `arg_comments` and `alt_doc_string`.

def format_docstring(elt, arg_comments:dict={}, alt_doc_string:str='', ignore_warn:bool=False)->str:
    "Merge and format the docstring definition with `arg_comments` and `alt_doc_string`."
    parsed = ""
    doc = parse_docstring(inspect.getdoc(elt))
    description = alt_doc_string or f"{doc['short_description']} {doc['long_description']}"
    if description: parsed += f'\n\n{link_docstring(inspect.getmodule(elt), description)}'

    resolved_comments = {**doc.get('comments', {}), **arg_comments} # arg_comments takes priority
    args = inspect.getfullargspec(elt).args if not is_enum(elt.__class__) else elt.__members__.keys()
    if resolved_comments: parsed += '\n'
    for a in resolved_comments:
        parsed += f'\n- *{a}*: {resolved_comments[a]}'
        if a not in args and not ignore_warn: warn(f'Doc arg mismatch: {a}')

    return_comment = arg_comments.get('return') or doc.get('return')
    if return_comment: parsed += f'\n\n*return*: {return_comment}'
    return parsed