Release reference: Add subschema definitions

[duncandewhurst]

OCDS 1.2 introduces revised definitions for subschemas like Award and Contract which contain important information not documented elsewhere (e.g. what types of framework agreement contract belong in the contracts array). As far as I can see, the subschema definitions only appear in the schema browser and not in the release reference. Since the text in the schema browser is not included in the search index and not all readers are expected to use the schema browser, I think the subschema definitions should also appear in the release reference (like in the development version of OC4IDS).

[jpmckinney]

Yes, good idea!