Specify what version of protocol the draft corresponds to

[mbakholdina]

It would be great to announce up high in spec what version this document draft refers to and how versioning will work in terms of forward and backward compatibility.
That was always a pain point with the HLS Pantos draft, and everyone still argues about version numbers and compatibility and requirements for what features need to exist in each version of the protocol.
For example, your current spec mentions version 4 and 5 of the protocol throughout, but the IETF document tool works in a different version (for the draft) numbering of 00 and 01.