create a new document containing all errata and additions to RFC 8794

[robUx4]

As discussed during our last IETF meeting, this should go in a new document which not an errata document nor a replacing RFC.

We need to collect all the PRs with errata label and put them in a new generated document.

[robUx4]

@SpencerDawkins sent a proposal for the format to follow with this document.

[robUx4]

Some followup emails on how to handle it: https://mailarchive.ietf.org/arch/msg/cellar/kCL24UZRcv-ySh3FTbPljNOlkQI/

[robUx4]

It looks like we should push this further. That may be needed to update the IANA registry. And IMO we should also do #164 so we can use it in Matroska v5.