[Blocked on expansion plate firmware update] Encoder motor: Add 'torque_limited'

[m-roberts]

Maybe this should run a loop and call a callback function passed by user?

[jcapona]

I don't think there's an Expansion Plate register for this, but I think that's the way to go for this one, that detects when the real motor speed doesn't match the target speed.

[duwudi]

justin is working on a status register at the moment - let's wait until he's implemented that