Support for Subject values

[stevenvegt]

Add support for Subject fields such as Locality and Organization so we can create VCs a did like this:

{
  "issuer": "did:x509:0:sha256:1b0961059b841654875d24545d0b93b37fd8a50c406a10a89702498f7e544b50::subject:O:De%20Regenboog:L:Hengelo::san:othername:2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344",
  "credentialSubject": {
    "subject:O": "De Regenboog",
    "subject:L": "Hengelo",
    "san:otherName": "2.16.528.1.1007.99.2110-1-900030787-S-90000380-00.000-11223344"
  }
}

[woutslakhorst]

The policyName/policyValue for the example above is:

subject,O:De%20Regenboog:L:Hengelo

Meaning the value string would have to be split to sub-key/values

[stevenvegt]

DID Syntax:

method-specific-id = ... ("::" policy-name ":" policy-value)

Voor subject policy:

policy-name     = "subject"
policy-value    = key ":" value *(":" key ":" value)

Vertaald naar een credential:

"credentialSubject": {
  $policy-name:$key: $value
}

of nested:

"credentialSubject": {
  $policy-name: {
    $key: $value
  }
}