Use official JSON schema

[aviks]

Currently the schema is generated from examples, which does not seem to be comprehensive. In one example I found, the Patient schema has a birthDate attribute, but since it's not present in the example used (patient-example-a.json), it does not appear in the swagger file.

You already have #5 which is similar, but I was wondering if doing directly to the published schema (https://www.hl7.org/fhir/fhir.schema.json.zip) might be best?

[rbren]

Definitely! I don't there was JSON Schema published when I first created this repo.

I would happily accept a PR that added these schemas.