Address @jyasskin's pre-Candidate Recommendation review comments

[msporny]

This PR attempts to address issue #1347 by making modifications to the specification based on @jyasskin's review:

2. Terminology

• Make section normative. [Fixed in e8a7c9f]

4.1 Getting Started

• Make section non-normative. [Fixed in cb3696e]

4.2 Contexts

• Remove ""each URL in the @context be one which, if dereferenced, results in a document containing machine-readable information about the @context." statement since it just describes how JSON-LD works (the data model for the spec). [Fixed in f62f40c]
• Clarify what "express context information" means. [Fixed in 52dfb8c]

4.4 Types

• Downgrade "All credentials, presentations, and encapsulated objects MUST specify, or be associated with, additional more narrow types" from MUST to SHOULD. [Fixed in 9b21005]

4.7 Issuer

• Update "the URL …, if dereferenced, results in a document … that can be used to verify the information expressed in the credential." to refer to controller documents. [Fixed in 6aa599c]

5.4 Integrity of Related Resources

• Update normative statements to say that the Accept header would be used for mediaType and the returned document would need to have that media type listed in the Content-Type. [Fixed in 9ebfe55]
• Specify that any relatedResource that fails content integrity protection results in a verification error. [Fixed in 8187708]

5.8 Zero-Knowledge Proofs

• Remove "The verifiable credential MUST contain a Proof" normative statement. [Fixed in 3a346e9]
• Delegate "not leaking information" to securing specifications. [Fixed in 3fdc1f7]
• Delegate "The verifiable presentation SHOULD contain a proof property to enable …" to securing specifications. [Fixed in 3a346e9, by not mentioning how to implement the securing mechanism -- which is up to the securing mechanism]

7.10 Validity Checks

• Add normative statements on CredentialStatus specifications to not enable individual tracking. [Fixed in fcfd9e5]

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Preview | Diff

[TallTed]

Relatively small. I think all are editorial. Some further tweaking may be necessary.

[jyasskin]

Just 1 substantive comment for this document; looks good once you've considered that.

[jyasskin]

Note that these restrictions will need to be enforced in the fix to w3c/vc-data-integrity#222. No need to block this PR on that.

[jyasskin]

This seems like it should be a MUST, but that MUST should appear in the place that uses the related resource, rather than here. The wording here could be something like

The authors of any specification that fetches a resource based on the `id`
of an object inside a <a>conforming document</a> need to consider whether
that resource's content is vital to the validity of that document. If it is,
the specification MUST produce a validation error unless the resource has
the expected media type and its bytes hash to the expected digest.

[msporny]

Applied a variation of your text in: 12f98c1

[msporny]

Normative, multiple reviews, changes requested and made, no objections, merging.

[iherman]

Normative, multiple reviews, changes requested and made, no objections, merging.

@msporny just flagging this: the VC Controller document MUST be published as a WD for the VCDM to go to CR. It is all right if it is published on the same day, but certainly not later.