Update the embedded copy of the expat XML parser to 2.1.0.  It brings
with it a vareity of bug fixes, both security and behavior.  See
http://www.libexpat.org/ for the list.

NOTE: I already backported the expat hash randomization fix in March.

Fixes issue #14340.
diff --git a/Misc/NEWS b/Misc/NEWS
index 74cd247..1ca70e1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -202,6 +202,8 @@
 Library
 -------
 
+- Issue #14340: Upgrade the embedded expat library to version 2.1.0.
+
 - Issue #11159: SAX parser now supports unicode file names.
 
 - Issue #6972: The zipfile module no longer overwrites files outside of