DOC : do not abuse enum markup

 - {ndarray, bool} -> ndarray or bool
 - {int, array of ints} -> int or array of ints
 - {str, function} -> str or function
 - {sequnce, int} -> sequence or int
 - {array_like, poly1d} -> array_like or poly1d
 - {None, list of `m` scalars, scalar} -> list of `m` scalars or scalar