Added memberReturns key (structAppend)

[Daemach]

Member functions can return different values.

[KamasamaK]

memberReturns is not the proper key for CF Docs. If you check out the JSON Schema, you'll see that member_details is what should be used for this.

[KamasamaK]

For member_details, the name and type are also required, which is why it is failing JSON validation. In this case, name would be append and type would be struct.

[pfreitag]

Thanks!