This commit brings the performance of the servo up quite a bit. It still
bounces, but I've increased the sample rate of the PID algorithm and
it's performing better now. The oscillations are much smaller because
the PID algorithm has more time to respond.

I'm seeing now why people say USB isn't a good control mechanism for a
servo. Every time I send a message via USB it eats a ton of clock
cycles. I think implementing a standard hobby RC servo protocol and/or
an I2C interface would be a good idea.