TODO

* Add to Scope classes: count/size

* Rename `new` methods, like Image.new or a relationship Recipe#newImage, to `insert` to adhere to CD name?
* Rename Schema to Model to adhere to CD name?
* The `class` of an association should be inflected from the name.
* Is it better to follow the original CoreData names such as the `optional` property of NSAttributeDescription, instead of using `:required` as the option?
* Currently Schema#to_ruby uses CFBundleVersion which should only change on each release. It might be better to use the build number so that migrations can be done more often.
* I’m not actually sure what should go in NSManagedObjectModel#versionIdentifiers.