Switch adapter to `resolve` instead of `fulfill`

[domenic]

Instead of calling it "fulfill" and saying "we promise to only call it as if it's the intersection of fulfill and resolve," we should call it "resolve" and give the same promise. This will reduce confusion from people thinking that they should implement pass-through fulfillment in their libraries in order to match the adapter interface.

This will be a backward-incompat change, but will go along well with the 1.1 launch.

[briancavalier]

+1