Function based road segment generation

[Joshuawd190]

Currently, the different road segments that can be added are manually defined.
So the more complex segments (like S curve or low rolling hills) are just a collection of add road calls with arguments

I think it'd be cool to define a road segment according to a pair of functions
One for the "height" of the road and one for the shape as seen from above.

y = f(z) as seen from the side
x = f(z) as seen from above

This would make it easier to add very silly roads and roads with more variety.

It is also more Math, so maybe that's a bad idea. (-_-;)