DOC: document default argument values for some arpack functions

closes https://github.com/scipy/scipy/issues/3829
this change, and similar ones below, aren't right. The type descriptor should use the actual type here (except if it's ``array_like``), so ``int`` and not ``integer``. See section 4 under https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#sections