Bring RELEASE-NOTES up to date
Bring RELEASE-NOTES up to date

The release notes file hasn't been touched since 2012, even though the code
has been changed, meaning that there's no proper documentation about what
changed over time for sysadmins and other users. This patch tries to identify
the meaningful changes made in these years (instead of adding each development
library and translation update) and prepends them to the file. Furthermore,
it revises the format to a wikitext-ish thing that you can work with better
n a text editor and possibly transfer to MediaWiki.org later without having
much remaining work to do.

Bug: T202953
Change-Id: Id2d8def45154ba2d88e92001daca3a4a6ab9b1dc

wikimedia/mediawiki-extensions-Variables,wikimedia/mediawiki-extensions-Variables