v3.0: River crossing options added!

Now at a river crossing, rather than just waiting to see if you cross successfully, you may choose to either:

- Take a ferry for $2 (non-free, risk-free)

- Caulk the wagon and float it across (free, low risk)

Due to the choice present, the risk of your wagon overturning has been increased to losing 4 food units, compared to the previous unavoidable 3-food-units-risk.