[CF-metadata] CF convention for vector quantities

[Jonathan Gregory]

Dear Bert et al.

I read Bert's original proposal carelessly - sorry. It was to introduce extra
dummy variables to point to components, rather than to take the component info
out of the standard names of the components.

I remain unconvinced about introducing this kind of information into the file,
as it cannot be depended upon if it is optional, so it doesn't help simplify
programs, and it is redundant because it can be deduced on the fly (I think).
However I know I have a general preference for clever programs and stupid
(though complete, correct and clear) files.

Cheers

Jonathan