Document /metadata differences between DSTU2 (and earlier) and STU3+

[kpshek]

Currently, the SMART documentation describes how a FHIR server advertises it supports SMART on FHIR via the old DSTU2 Conformance resource. With STU3, this resource was renamed to CapabilityStatement.

We need to:

1. Update the SMART documentation to distinguish between the two
2. Provide guidance to SMART app developers on how to determine from an iss (FHIR base URL) what version of FHIR they are dealing with and how to read the /metadata data

[jmandel]

I'm not sure the iss itself conveys this information, unless you're considering some kind of naming convention? I think the recommended approach would be to fetch /metadata and see — this would be my preference over a naming convention (which is brittle) or a third URL parameter to convey version (which might always be wrong / out of sync with reality).

[kpshek]

@jmandel - Sorry, my initial description wasn't clear. I realize the FHIR base URL (iss) doesn't convey the FHIR version. I was trying to say that we need to provide guidance that SMART app developers will need to call iss/metadata and determine the version of FHIR they are dealing with.