2021 February 27 Breaking Changes Changelog (#11975)

* restore main readme.md

* add ChangeLog entry for 2021-02-27 develop branch - initial version

* update Docs; consolidate sidebar entries to new Breaking Changes History doc

* Changelog update

- concatenate similar changes as one list item
- unify change formatting (remove [bracketed] headings and trailing periods)
- item sorting improvement

* update Changes Requiring User Action section

Detail the changes regarding keyboard relocations/additions/deletions.

* add entry for fauxpark's user keymap cleanup for config.h/rules.mk

* add link to Jacky Studio bugfix PR

* add link for "ChibiOS conf migrations... take 15"

* add links for "Make LAYOUT parsing more robust" and "Massdrop develop rgb fix"

* remove sort sequence numbers

* rename Breaking Changes History page

Renames the Breaking Changes History page to "Past Breaking Changes".

* update schedule in Breaking Changes Overview

* suggestions/changes per tzarc

* skully's changes

* add entry for "Fix develop" (PR 12039)

Co-authored-by: Nick Brassel <nick@tzarc.org>
Co-authored-by: Zach White <skullydazed@gmail.com>

docs/_summary.md

@@ -119,12 +119,8 @@
   * Breaking Changes
     * [Overview](breaking_changes.md)
     * [My Pull Request Was Flagged](breaking_changes_instructions.md)
-    * History
-      * [2020 Nov 28](ChangeLog/20201128.md)
-      * [2020 Aug 29](ChangeLog/20200829.md)
-      * [2020 May 30](ChangeLog/20200530.md)
-      * [2020 Feb 29](ChangeLog/20200229.md)
-      * [2019 Aug 30](ChangeLog/20190830.md)
+    * [Most Recent ChangeLog](ChangeLog/20210227.md "QMK v0.12.0 - 2021 Feb 27")
+    * [Past Breaking Changes](breaking_changes_history.md)
 
   * C Development
     * [ARM Debugging Guide](arm_debugging.md)