Added vehicle run-over damage

I added run-over damage for tanks and jeeps. They can drive through hostile infantry, while friendly infantry are still treated as bodies to avoid.

Impact damage grows with the vehicle mass and the square of its speed. Surviving infantry are pushed aside and can be knocked down, with resistance affected by the unit and its stance.

“A moving tank should matter even before its gun fires.”

I set up a tank and a short hostile infantry line, then issue a normal move order through them with the tank holding fire. The soldiers are pushed apart and survive the pass, making the collision easy to distinguish from a gun attack.