Improve structure of specification

[danielfett]

To fix Issue #290, this PR reorganizes what was previously section 5 as follows:

[danielfett]

Note: I also changed the story in Section 5 from a bottom-up to a top-down approach (structure of compact serialization SD-JWT first, then going into the details).

[Sakurann]

The Decoy Digests, Hash Function Claim, Holder Public Key Claim subsections feel a bit out of place in section 7. What would you think about moving them to subsections under 5.1. Issuer-signed JWT Payload?

+1 to this

[danielfett]

I made the additional changes proposed by Brian, with the following deltas:

• I moved the section "Decoy Digests" to be the last subsection of "5.2 Disclosures". It did not make sense in 5.1 as not all concepts were introduced there yet.
• I slightly reformatted the list of requirements on the SD-JWT payload in Section 5.1.
• I noticed that the note on line breaks in the examples is not in the correct place and moved it towards the beginning of Section 6 (Example 1).

Editor's copy link: https://drafts.oauth.net/oauth-selective-disclosure-jwt/danielfett/fix-290-new-structure/draft-ietf-oauth-selective-disclosure-jwt.html

[bc-pi]

I moved the section "Decoy Digests" to be the last subsection of "5.2 Disclosures". It did not make sense in 5.1 as not all concepts were introduced there yet.

That makes sense and is better than what I'd suggested.