[uf-new] hProduct: Suggested changes to proposed fields

[Paul Lee (이기수)]

Based on work on examples and brainstorming, what about the following
suggestions?

- bump sku, upc, isbn to top level, also optional (agreement with Jay
Myers on sku)
- drop uid (since this seems to replicate sku, per the examples page)
- add condition, mpn to top level, also optional

Paul

-- 
Paul Lee
Google, Inc.
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