This game is based loosely on the arcade classic of the late 70's called "Ripoff".
The idea is simply to protect your barrels from the enemy tanks.
Shoot them, run into them, get them to shoot each other -- it doesn't matter,
just protect your barrels from them.
Once an enemy locks onto a barrel, they will try to drag it outside the game
field where it will be beamed up to their space station and presumably the world
would be a worse place for it, so don't let it happen.
The game is over when all barrels have been transported to the enemy space station.
Collect power-ups to enhance your tank's weaponry. Be careful, enemy tanks can
also power-up. Power-up's last the duration of the tank's life and are cumulative.