Rethink definition / term relationship and naming

[scottaohara]

The relationship for a term/definition is defined in the spec by creating an aria-labelledby or nesting relationship with the definition to the term.

If I recall correctly, the naming idea was so that a definition could be associated with its term. but looking at this now as i'm going through the roles / how they can be named, i'm not really sure why we didn't use aria-details instead?

Also, I thought it odd that at term could get name from author, but i realize that might be because of these previously being considered standins for dt and dd elements, but that was also rethought when working on aria 1.2.