link the 2020 Feb 29 Breaking Changes changelog from the summary

docs/_summary.md

@@ -109,6 +109,7 @@
     * [Overview](breaking_changes.md)
     * [My Pull Request Was Flagged](breaking_changes_instructions.md)
     * History
+      * [2020 Feb 29](ChangeLog/20200229.md)
       * [2019 Aug 30](ChangeLog/20190830.md)
 
   * C Development