Figure out how we handle 'quiz' type challenges

These are just reading assignments but it would be nice to have a set of questions at the end of each one that helps to ensure the user has grasped the concept. Suggestions welcome but we could probably go ahead and build out a quiz type experience within the CLI. Users should be graded on their answers and only pass if they make make a grade better than 80% correct. All of this is subject to new and better ideas.

Start by reviewing the existing CLI challenge flow and how reading assignments are represented. Define the quiz experience, question and answer handling, grading rules, and passing behavior; done means the scope is agreed and users can complete and be graded on a quiz.

Written by the indexing model from the issue text.