schema updates for 3.0.4

[karenetheridge]

The 3.0.4 schemas need a review pass for accuracy.

• update $comment, description and $id URIs for v3.0.3->v3.0.4 (where can an html preview of the specification be viewed?)
• ensure links in specification (referencing schema files) are correct
• compare specification and schema diffs from 3.0.3 and 3.0.4, thinking about any spec changes that haven't yet been reflected in the schemas, and what changes have been made to the schemas already and confirm they are accurate (this SHOULD be a no-op, but mistakes have occasionally happened before ;) )
• ensure the .json and .yaml files are consistent
• verify validity against the draft4 json metaschema
  (I am converting locally to draft7 so as to allow: apt-get libjson-schema-modern-perl; json-schema-eval --strict --validate-schema schemas/v3.0/schema.json)

[handrews]

There are definitely improvements to be made to the 3.0 schemas, but there aren't any schema-impacting differences between 3.0.3 and 3.0.4. The only version-ish thing that should change is the date in the $id of the schemas.

AFAIK, this is true across 3.0.0 - 3.0.4, and any schema applying to one applies to all and should only mention 3.0 in comments or other text (no patch release number). Some might make an argument regarding nullable in 3.0.0 – 3.0.2 va 3.0.3 – 3.0.4. However, the official position is that the clarifications to nullable in 3.0.3 were only clarifications (it made the relationship between nullable and type behave the same way as the relationship between draft-04 exclusiveMinimum and minimum (and exclusiveMaximum and maximum).

Schemas can be viewed on the spec site. I didn't think to comment on it in the 3.1 schema issue, but I'm pretty certain the spec should just link to this page and not to anything specific. (For those not familiar with the history of "latest" schemas, we should not have a "latest" schema symlink because refining the constraints to be more accurate could cause automated systems to suddenly invalidate previoulsy-valid OADs which is not a nice thing to do – we tried this several ways with the JSON Schema meta-schemas before deciding on the date-based $ids to avoid ever changing a schema in place).