* Implement gomatrixserverlib.HeaderedEvent, which should allow us to store room version headers along with the event across API boundaries and consumers/producers, and intercept unmarshalling to get the event structure right
* Add federationsender to previous
* Pass cfg by reference around the codebase
* Merge branch 'master' into pass-cfg-by-ref
Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>