changes file for big free macro-ization branch

changes/bug24337

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+  o Minor features (defensive programming):
+    - Most of the functions in Tor that free objects have been replaced
+      with macros that free the objects and set the corresponding pointers
+      to NULL. This change should help prevent a large class of dangling
+      pointer bugs. Closes ticket 24337.
+
+    - Where possible, the tor_free() macro now only evaluates its input once.
+      Part of ticket 24337.