did-spec-registries update

The standard review of did-spec-registries shows significant changes in the relationships. A thorough review of the specification needs to be performed. Items noted on a quick review were

• implements connections to signature types seems to no longer exist in the document. This is the intermediate did-spec-registries-1-of-a relationships on the map
• verification method types such as JsonWebKey2020 and RsaVerificationKey2018 are arguably references entries that are not currently mapped. Whether references that are used only for the value of a property should be included or left out to simplify complexity of the map is open to interpretation and may not be entirely consistent across all the specifications' mappings.