Update ChangeLog and Release Notes from previous pull requests

ChangeLog

@@ -1,3 +1,15 @@
+2022-09-01  Jay Berkenbilt  <ejb@ql.org>
+
+        * More optimizations and cleanup from m-holger (#726, #730)
+        including major refactor of QPDF's internal representations of
+        objects. In addition to a large performance improvement, this also
+        made it possible for QPDFObjectHandle::getOwningQPDF() to return a
+        null pointer if the owning QPDF had been destroyed. (A more
+        complete solution to this problem will be introduced for qpdf 12.)
+        This work also paves the way for a future alternative to
+        QPDFObjectHandle that is more idiomatic C++ and has greater type
+        safety.
+
 2022-08-31  Jay Berkenbilt  <ejb@ql.org>
 
         * From m-holger (#729): refactor QPDF's parser into a new

manual/release-notes.rst

@@ -12,7 +12,7 @@ For a detailed list of changes, please see the file
     - Many performance enhancements have been added. In developer
       performance benchmarks, gains on the order of 20% have been
       observed. Most of that work, including major optimization of
-      qpdf's lexical layer, was done by M. Holger.
+      qpdf's lexical and parsing layers, was done by M. Holger.
 
   - Replacement of ``PointerHolder`` with ``std::shared_ptr``
 
@@ -178,6 +178,12 @@ For a detailed list of changes, please see the file
       ``replaceKeyAndGetOld``, a ``null`` object if the object was not
       previously there.
 
+    - The method ``QPDFObjectHandle::getOwningQPDF`` now returns a
+      null pointer (rather than an invalid pointer) if the owning
+      ``QPDF`` object has been destroyed. This situation should
+      generally not happen for correct code, but at least the
+      situation is detectible now.
+
     - Add new ``Pipeline`` methods to reduce the amount of casting that is
       needed:
 
@@ -247,6 +253,9 @@ For a detailed list of changes, please see the file
       some additional caching to reduce the overhead of repeatedly
       reading environment variables at runtime.
 
+    - Lots of code cleanup and refactoring work was contributed in
+      multiple pull requests by M. Holger.
+
 10.6.3: March 8, 2022
   - Announcement of upcoming change: