Use Differential Drive

[duane701]

I high jacked Nic's branch.

We should practice tomorrow with the changes for TankDrive.

This uses the DifferentialDrive::TankDrive capability which has some nice functionality we've never had:

• squared inputs. This gives you more control at slow speeds and fast response at high speeds. Try adjustments at slow speeds to see how you like it. The gear shift is still in, see if you like it or not.
• dead band. Any values smaller than .02 are zero. The rest of the range is scaled to fill the entire range. The dead band will help to prevent the robot drifting when you let go of the joystick.

Try these changes. We can always reverse or adjust them.

[duane701]

This is what the squared input looks like.