* Remove entries which don't affect the rendered spec (sorry people using the swagger schemas - we'll have to figure out a changelog for you). See https://github.com/matrix-org/matrix-doc/issues/3475
* Note that a breaking change is removed by this commit: key backup was introduced in this release cycle, so is not breaking.
* Use uniform references to MSCs ("as per MSC0000").
* General rewording to be consistent with the overall voice of the changelog.
* Condensing of entries where needed to make them fit in the changelog.
* Rewording to collapse entries into fewer lines.
* Spell "deprecation" correctly in file extension.
