more gears

since there are cars with eight gear transmissions out there (consumer ones; i have no idea how many gears larger vehicles have, but i'd suspect maybe more than consumer cars?), it seems like the gear_lever_position should at least go up to eighth. i am proposing to add two more gears just to be on the safe side.

transmission_gear_position already went up to eighth, but if gear_lever_position is adjusted to go up to tenth, then maybe adjusting transmission_gear_position to the same upper bound makes sense.