[opus] Channel Mapping Family for Ambisonics

[Timothy B. Terriberry]

Michael Graczyk wrote:
> Would you mind giving me a more specific example of the sort of document
> that you think this should look like? I'd like to write up something
> that is somewhat final.

I don't have a specific one for an Opus channel mapping, no. RFC 7845 
itself is an example of a document that adds a new codec mapping to the 
Ogg container. Similarly, RFC 7587 is an example of a document that adds 
a new payload format to the RTP protocol. Hopefully those are enough of 
an example to use for flavor and required sections like IANA 
Considerations, Security Considerations, etc.

You can find the XML source for both documents in the Opus git repository.