HullPixelBot can now turn corners

Spent a bit of time today fiddling with timer interrupts so that I can get fine control of the speed of the motors on the HullPixelBot. Because they are steppers they are quite precise, which means I can get the bot to trace accurate curves. 

The next thing I have to do is put the light and distance sensor on the front (along with a bumper) and then we'll have a proper robot.