***Apologies that this code is not all that well written.
It was quickly changed from a version using no classes/Sprites, and
should be redesigned somewhat.

One side-effect of teh changes were the border crashes are now 'off by one'
and need a fix (an exercise for the reader).

The purpose of this example is to show how a class can maintain a list/group of sprites,
and to show how movement can be restricted to grid-like coordinates.  The way the
tail of the snake moves in the same past locations as the neighbouring cells is a nice
exercise to isolate as well (can be used in a variety of contexts).

Finally, a second version of the game is made to handle input from a DDR Dancepad (or
a standard controller will also work).  This illustrates the impact that the input
device can have on the gameplay, and can promote some real creativity for other games.
Be prepared for hilarity, and broken ankles.
