Red chapter 5 exercises

Chapter 5 exercises, answers and _Try This_ tweaks.
It's an object that wraps the `message` array to make it easy to later print out the arrays contents with just `join.get()`. `collect` takes a `Collector` that builds up a result from each element of a stream, `Collectors.joining` provides a `Collector` that joins each `String`, placing the delimiter between each.