PixelArcade - a simple menu to select which game to play

It's a bit of hack, but it is a first run at merging games so you can pick which game to play
without having to download a new program.  The 'PixelArcade.ino' currently includes:

TheGreatRace
SnakePixel
SuperPixelBros
SpaceInvaders
Connect4
PixelBird
Dice2

(above comes to just about 17k)

This PR includes a small perl script, merge-games that does the actual merging.  It uses a pseudo pre-processor tag in the .in file to merge, deconflict some globals, and create the .ino that can be compiled.