Interactively check the current buffer for doc string errors.
Prefix argument START-HERE will start the checking from the current
point, otherwise the check starts at the beginning of the current
buffer. Allows navigation forward and backwards through document
errors. Does not check for comment or space warnings.
Optional argument SHOWSTATUS indicates that we should update the
checkdoc status window instead of the usual behavior.
(fn &optional START-HERE SHOWSTATUS)