Fix the find_rss_doc() so that it can locate the correct file
Replace __builtin__.file type check with a call to PyFile_Check
Comparing against _io._IOBase (compiled) is faster than io.IOBase (pure)
Replace collections.Iterator reference with checks for '__iter__' and 'next' methods
Make in_dict and in_slots inline
itemgetter always returns unicode
Module names might be unicode, so change the type hint to object
Move doctests for is_type and is_object to the test_util module
Make the is_picklable function inline