Implement odometry

[wxb1ank]

We need to track the robot's position relative to the hubs for the purpose of automated shooting. See the WPILib docs for how this can be done with a little math. We will probably want to put the odometry-updating code in one of the Robot::periodic* methods.

[wxb1ank]

This may not be strictly necessary; we could use the ta (target area) output from the Limelight camera to determine the distance of targets (e.g., cargo, retroreflective tape) with the inverse square law.

But, having seen the output of the Limelight, I think its reported position of the target is far more accurate than the area.

[SomeoneMysterious]

As far as I've heard/remember, the team is planning to shoot from a constant distance from the hubs. However, this might still be useful and needed depending on the situation, but for right now I don't think it will end up being needed. Let me know if you guys have heard otherwise, however.

[BowlesCR]

Should be able to get something useful out of the NavX displacement... it does drift, but should be accurate to within a few inches over the course of the match.