[docs] asyncio.docs: Document subprocess_exec and subprocess_shell (issue 20694)

[guido at python.org]

http://bugs.python.org/review/20694/diff/11109/Doc/library/asyncio-eventloop.rst
File Doc/library/asyncio-eventloop.rst (right):

http://bugs.python.org/review/20694/diff/11109/Doc/library/asyncio-eventloop.rst#newcode470
Doc/library/asyncio-eventloop.rst:470: .. method::
BaseEventLoop.subprocess_exec(protocol_factory, \*args,
stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
universal_newlines=False, shell=False, bufsize=0, \*\*kwargs)
Please remove universal_newlines, shell and bufsize from this signature
(and also from the next one).

http://bugs.python.org/review/20694/diff/11109/Doc/library/asyncio-eventloop.rst#newcode479
Doc/library/asyncio-eventloop.rst:479: list of strings,
:func:`subprocess_exec` takes multiple string arguments.
Maybe add "similar to os.execl()"?

http://bugs.python.org/review/20694/diff/11109/Doc/library/asyncio-eventloop.rst#newcode503
Doc/library/asyncio-eventloop.rst:503: * *bufsize*: The buffer size to
be used when creating a pipe; this is
I don't actually see a use case for setting this nonzero on any
platform, as buffered I/O doesn't mesh well with async I/O. I'd rather
not call it out in the argument list, but instead add a note to the next
bullet saying "(however, *bufsize* should be omitted or zero)". The same
is true for shell and universal_newlines -- they are only present in the
signature so we can explicitly check that they aren't set to different
values than what we need. Maybe it makes more sense to give an explicit
list of the parameters that *do* make sense to pass to Popen?

http://bugs.python.org/review/20694/diff/11109/Doc/library/asyncio-eventloop.rst#newcode525
Doc/library/asyncio-eventloop.rst:525: the arguments.
the remaining arguments.

http://bugs.python.org/review/20694/