bpo-33504: Migrate configparser from OrderedDict to dict. (#6819)

With 3.7+, dictionary are ordered by design.  Configparser still uses
collections.OrderedDict, which is unnecessary.  This updates the module
to use the standard dict implementation by default, and changes the
docs and tests to match.
diff --git a/Misc/ACKS b/Misc/ACKS
index 42f1abc..481385f 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1315,6 +1315,7 @@
 John Redford
 Terry J. Reedy
 Gareth Rees
+John Reese
 Steve Reeves
 Lennart Regebro
 John Regehr