Create a JSON Schema definition for a DID Log Entry

[swcurran]

Define a JSON Schema definition for a DID Log Entry, including all of the possible parameter attributes. Include a link in the spec to the JSON Schema.

[swcurran]

@PatStLouis -- is this a good one for you? I think you've done a fair amount of JSON Schema work previously, right?

[swcurran]

Resolved by #206. Leaving open until the JSON Schema is referenced in the spec.