Migrate API changelog from HTML into Markdown

Managing the API changelog in HTML has been rather burdensome, getting
the formatting correct and doing things like having numbered lists
added unneeded burden to the process.

This change moves all the old content to markdown and
places it prominently next to the other NewAndNoteworthy content.

Also included here is some fine tuning to the related documentation
about API.

Part of eclipse-cdt#32

NewAndNoteworthy/CDT-11.0.md

@@ -10,6 +10,10 @@ This is the New & Noteworthy page for CDT 11.0 which is part of Eclipse 2022-12
 
 Jave 17 is now required to build and run Eclipse CDT. See https://github.com/eclipse-cdt/cdt/issues/80
 
+# API Changes, current and planned
+
+Please see [CHANGELOG-API](CHANGELOG-API.md) for details on the breaking API changes in this release as well as future planned API changes.
+
 # Bugs Fixed in this Release
 
 See [GitHub milestones](https://github.com/eclipse-cdt/cdt/milestone/2?closed=1) and for bugs that haven't been transitioned to GitHub please see Bugzilla report [Bugs Fixed in CDT 11.0](https://bugs.eclipse.org/bugs/buglist.cgi?bug_status=RESOLVED&bug_status=VERIFIED&bug_status=CLOSED&classification=Tools&product=CDT&query_format=advanced&resolution=FIXED&target_milestone=11.0.0).