Difference Engine v2.0

Babbage's Difference engine. Can calculate polynomials.

Animation: http://www.youtube.com/watch?v=8X6iIpjawZU

This is a revision of thing 7609, but is not compatible.

This in incomplete.

Parts Remaining
-
* Carry Mechanism
* Timing/Lift Mechanism
* Detents for wheels (prevents unwanted rotation)
* Thrust bearings