Flood track

I merged in the first version of the Flood track, making the Country championship the first one to be composed of three tracks.

New vehicle

I started to work on a new vehicle and decided to add a monster truck. But a monster truck requires huge tires, so I added the ability to define tire size per vehicle axle. Extending the vehicle definition was easy, but during the initial tests it did not look quite good because until now the game only drew the shadow for the vehicle body, not for the wheels. This was OK with small tires, but looked odd with huge ones. A first naive implementation made it look better, but caused overlapping shadows, like that:

Note: I do not intend to fit Red with huge tires like this, this is just for testing purposes!

After some rework of the engine to draw all vehicle shadows in a separate frame buffer, shadows look better: