Move UserString to collections.
Removed decode() method. Added isidentifier() and format() methods.
Drop MutableUserString class.
diff --git a/Misc/NEWS b/Misc/NEWS
index 26cc2db..1a3ae21 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -1650,7 +1650,8 @@
XXX their API still needs to be modernized (i.e. eliminate the iter methods).
- Created new UserDict class in collections module. This one inherits from and
- complies with the MutableMapping ABC.
+ complies with the MutableMapping ABC. Also, moved UserString and UserList
+ to the collections module. The MutableUserString class was removed.
- Removed UserDict.DictMixin. Replaced all its uses with
collections.MutableMapping.