Adding projects 21 and 22.

Corrections for Swift on Sundays 1 book.

Adding Switcharoo episode.

Merge pull request #2 from deirdresm/019_macOSContextFix

Fix crash that occurs because persistentContainer isn't established quite early enough.

Added Dad Jokes episode.

Adding Terminal Wizard episode.

Added Untangler episode.

Added JustType episode.

Added WatchReactions episode.

Added SpotTheScientist episode.

Added TextTransformer project.

Added MultiMark episode.

Added Zaptastic episode.

Added Create ML playground.