Issue #21741: Add st_file_attributes to os.stat_result on Windows.

Patch by Ben Hoyt.
Tulip issue 83: document more asyncio functions in docstrings
(Merge 3.4) Tulip issue 83: document more asyncio functions in docstrings
#21690: fix a couple of links in the docs of the re module.  Noticed by Julian Gilbey.
#21690: merge with 3.4.