bpo-37759: More updates to Whatsnew 3.8 (GH-16854)

* math.perm() and math.comb()

* math.isqrt()

* Add singledispatchmethod()

* itertools.accumulate()

* Optional headers for xmlrpc.client.ServerProxy

* IDLE non-BMP characters

* import collections.abc directly

* @coroutine is deprecated

* pprint.pp()

* New options for object.__reduce__()

* DictReader no longer returns OrderedDicts

* "force" option for logging.basicConfig()

* Fix spelling

* cProfile context manager

* Various markup/grammar fixes from Kyle Stanley.
Other minor fixes as well.
Also, dedup the __reduce__ entry.

* Fix markup

* Fix grammar nits found by MS Word