Clear change log and update documentation
Created by: matthew-d-jones
- Cleared changes documented in v3.0.0 release from the changes log (changes.md)
- Updated status message documentation, which I forgot to do when implementing FlatBuffer serialised status messages. (Closes DM-1968)
I've pushed the commits to the release-3.0 branch and cherry-picked them from there in to this branch. This ensures someone looking at the release-3.0 branch sees the correct documentation for that version.