Add documentation for the GameProducer class in the Game Kit.

This documentation was provided by Omri Barak, a student participating
in Google Code Initiative (GCI) 2011.

Signed off by John Scipione

Since this is the first class documented in the Game Kit I also added
a reference to the Game Kit to the API docs front page.

docs/user/book.dox

@@ -32,6 +32,8 @@
 		- The \ref app is the starting point for developing applications
 			and includes classes for messaging and for interacting with
 			the rest of the system.
+		- The \ref game provides classes for producing game sounds and
+			working with full screen apps.
 		- The \ref interface is used to create responsive and attractive
 			graphical user interfaces building on the messaging facilities
 			provided by the Application Kit.
@@ -97,6 +99,11 @@
 		- BRoster
 
 
+	\defgroup game Game Kit
+	\brief The Game Kit provides classes for producing game sounds and
+		working with full screen apps.
+
+
 	\defgroup interface Interface Kit
 	\brief API for displaying a graphical user interface.