The app after making final changes recommended by tech reviewers.

This version of the app therefore corresponds to the state of the code at the end of Chapter 12 in the book.
Notice that there a plenty of refactoring steps taken through the course of the worked example, so if you're
looking at a chapter and can't reconcile the source code in the text with how it looks in the repo, check
the commit history for the file to see if it was refactored. This will particularly be true for the test
fixtures, in which method-local variables are often pushed into ivars managed in -setUp and -tearDown.

This version corresponds to the draft manuscript being complete.