Six code files for Chapter 4:

	- EventTester.cs: The first example code attached to the Play button. It outputs most of the events in Unity's console.

	- ShowTooltip.cs: The script added to any GameObject which needs to display a tooltip.

	- DisappearOnClick.cs: Attach this script to any GameObject to make the desired target disappear when it's clicked. You can select a method to call when it's finished disappearing.

	- MenuManager.cs: Updated version of the MenuManager.cs script attached to our UI Root.
Now derives from Singleton class.

	- Singleton.cs: The class that makes any class that derives from this one a singleton, accessible through Class.Instance, that will persist through scene changing.

	- ToggleInit.cs: Attach to the sound checkbox. Makes sure the volume sliders are hidden at start if ever the sound was disabled at start.