Vector-valued Quantities

[David Berry]

Ed,

> It would be most straightforward if the serialization ends up looking
> something like.
>
> starDescription {
>     luminosityQuantity
>     massQuantity
>     }

But then StarDescription is not a CoreQ because a CoreQ is a
Frame + Mapping, and there is no sign of a Frame or a Mapping in the
above.

David