merge Result and Evaluation

[dave-doty]

Currently, there is a class Result that is returned by the evaluate function of a Constraint, and there is a related class Evaluation that contains (I think) all the information in a Result, plus additional information.

This seems redundant. We should just have evaluate return an Evaluation, with most of the fields not yet specified, and the search algorithm can later populate those fields rather than making a whole new object.

I think the reason they are separate is that I used to make an Evaluation only for constraint violations, whereas a Result was created for every evaluation of a constraint. However, that's no longer the case. We keep a list of all Evaluation's. But there still might be a good reason to keep these as separate classes.