Fix boundaries and add to the game code.

[buxtonpaul]

Fix the boundary code so that the boundaries are at the edge of the screen.

Add the missing boundary code to the automata code. The book specifically mentions that we have added boundaries, but the sample code in the chapter doesn't add it.

[buxtonpaul]

In general this chapter of the book has some issues. Whilst introducing the idea of a test harness at this point makes sense, not incorporating it into the development of the code means that if we use the test harness as is then we cannot follow along easily with the book as the code we are adding is not compatible with the test harness code.
The test harness also introduces some patterns that are not covered in the book (such as use of Box) which are important to understand.
It would be better to also add the test harness as an additional binary that uses the same code as the game rather than a separate folder with its own copy of the code.