Document the difference between ResolutionDetails and EvaluationDetails

[justinabrahms]

They look really similar in the spec (types.md especially). Maybe say what the difference is?

[moredip]

Relatedly, types.md currently says:

NOTE: The resolution details structure is not exposed to the Application Author. It defines the data which Provider Authors must return when resolving the value of flags.

Which I found pretty misleading since the Application Author does get access to the evaluation details structure, which are basically a superset of the resolution details structure.

I think maybe the intent was to say that the Application Author doesn't have direct access to actual instance of the resolution details structure which was provided by the provider. Either way, I was confused.