prboom: add new games package PrBoom

This patch adds a new package PrBoom. PrBoom is a Doom and Doom ][ client which
uses the SDL library for graphics, sound and network. It also supports OpenGL,
but this has not been enabled in this package since few embedded platforms
support OpenGL.

PrBoom allows you to play the good old game on newer hardware. It even supports
higher resolution and better rendring, while still keeping the old style alive.

http://prboom.sourceforge.net/



Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>