Implement farmer.

[mklingen]

• [x] Basic farmer movement.
• [x] Fence building.

On fence building: farmer should briefly pause while building a fence. Fence then appears in the cell that the farmer was previously in.

Building a fence consists of pushing on the control stick while holding a button (you build fences in a "direction")

• [ ] Shoving sheep slowly.

[mklingen]

Farmers are now just AI.