.select on create or update of a model.

It would be nice to be able to select the returned fields from a create/update request.

eg.

```
myModel.create(data).select('name.first').exec(function (err, data) {
//Data only has name.first
});
```

Start at the model create and update entry points and follow the execution path used by the shown .select('name.first').exec example. Compare how returned fields are handled for both operations. Done means the callback data for create and update contains only the selected field, with the behavior covered by the relevant existing tests.

Written by the indexing model from the issue text.