Support a JSON schema (inline or as a URI reference) as a format option for Table Schema fields of type object and array

[costas80]

We use Table Schema to define requirements on CSV content and find currently that fields defined as object or array are rather weak. The Table Schema spec says that either or these should simply be well-formed JSON objects or arrays (respectively).

It would be a good improvement to allow object and array fields to have a JSON schema defined as part of their format definition. The JSON schema could be provided:

• Inline for simple cases.
• As a URI reference where external schemas are available.