Create Item API

The new "Item" API relates somewhat to some community postings about being able to properly track the values from mutation operations.

The Item structure itself is fairly simple and is simply a logical extension of the ValueResult API (no defaults are changed and the Item object can be used as a ValueResult object).

The changes are in the ability to pass an already-created Item and receive it back, therefore eliminating a potential "conversion" step.

Another thing this API does is add a consistent means by which to specify per-item options for *_multi operations.