Update FieldModel.values to support parameters

Previously only a query parameter was supported. This has been
changed to support an arbitrary set of parameters. Further, although
passing a callback is still supported, the preferred method is registering
handles with the returned promise.

For example:

f.values({limit: 0}).done(function(values) {
    // do something...
});

Fix #425
Fix comment about shifting arguments
Merge pull request #429 from cbmi/issue-425

Update FieldModel.values to support parameters