Clarify issues with case insensitive digests resulting in repeated digests

[zimeon]

Consider https://github.com/OCFL/fixtures/tree/master/1.0/bad-objects/bad16_digest_repeated which has inventory:

{
  "digestAlgorithm": "sha512",
  "head": "v1",
  "id": "ark:123/abc",
  "manifest": {
    "cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e": [
      "v1/content/empty1"
    ],
    "CF83E1357EEFB8BDF1542850D66D8007D620E4050B5715DC83F4A921D36CE9CE47D0D13C5D85F2B0FF8318D2877EEC2F63B931BD47417A81A538327AF927DA3E": [
      "v1/content/empty2"
    ]
  },
  "type": "https://ocfl.io/1.0/spec/#inventory",
  "versions": {
    "v1": {
      "created": "2019-01-01T02:03:04Z",
      "message": "Example with two empty files that thus have the same digest but are represented with different normalizations",
      "state": {
        "cf83e1357eefb8bdf1542850d66d8007d620e4050b5715dc83f4a921d36ce9ce47d0d13c5d85f2b0ff8318d2877eec2f63b931bd47417a81a538327af927da3e": [
          "empty1"
        ],
        "CF83E1357EEFB8BDF1542850D66D8007D620E4050B5715DC83F4A921D36CE9CE47D0D13C5D85F2B0FF8318D2877EEC2F63B931BD47417A81A538327AF927DA3E": [
          "empty2"
        ]
      }
    }
  }
}

the digests are actually the same but in both manifest and state one is in uppercase and the other in lowercase. This could be allowed (should be text explaining merge after normalization) or it could be forbidden (what I'd assumed, should be text explaining that different normalizations MUST not result in repeated digests)

[zimeon]

See #437 where we decided to keep case insensitivity

[awoods]

Given the previous decision (#437 (comment)), do we want to add "text explaining merge after normalization", or do nothing?

[zimeon]

I'm inclined to require consistent normalization within a single inventory.json but I think we have to add explanation either way

[neilsjefferies]

As per Community Call 13/5 - digest should occur once within a manifest regardless of case

[zimeon]

Closed by #468 and #469