Adding CBOR Headers and Serialization

[dwaite]

First pass at what might be considered "proper" CBOR support.

Incomplete list of tasks:

• Algorithms registry to take into account numerical algorithm identifiers in CBOR
• Nonce resolution due to rules added by EATS - do we keep the very different format requirements or adopt one/the other.
• Additional editorial pass on the proof document
• Align changes on each document
• Change proof_jwk to proof_key and presentation_jwk to presentation_key (see: Change Issued JWK / Presented JWK Protected Headers #142 )
• Change "The compact serialiation provides a space-efficient encoding" to "The compact serialization provides a JSON-based space-efficient encoding".
• Add the missing IANA.MediaTypes reference.

Goal is to get this shared in advance for discussion/revision during 121. One overarching question is whether we try to further consolidate to have the headers have a consistent data model and rules, even if that means further deviating from JOSE rules for the similarly-named headers.

[selfissued]

Please apply my change suggestions, then I'll approve.

Let's also change proof_jwk to proof_key and presentation_jwk to presentation_key throughout because it's odd having _jwk named things referring to COSE_Key objects.

Please change "The compact serialiation provides a space-efficient encoding" to "The compact serialization provides a JSON-based space-efficient encoding".

Please add the missing IANA.MediaTypes reference.