DOC: update Changelog ready for release

First pass at Changelog - anyone remember stuff I missed?

Any more credit that should go in there?  Please add yourself if I
forgot you.
Merge branch 'pre-release-changelog' into main-master

* pre-release-changelog:
  DOC: update Changelog ready for release
DOC: update changelog

With new API for caching, parrec2nii changes.