Fixing AI for the new year!

I wasn't happy with the AI in the last update. So I fixed it.

It was actually quite a bit of work, trying to make some smart enough avoidance in a completely cheated environment. It's one of those situations where having an actual 3D space would help... At least now I had to be creative and would refrain from making it perfect. I ended up writing 2 very different versions and picking the best.

In addition of the avoidance, I also tweaked the steering and 'keep center' behaviour, and how they all mix. That completes the 3 main behaviours, so we could say it's an extensive AI update!

As a side note: unlike most racing games of the past (or current ones, but for totally different reasons), the whole simulation is still entirely non-cheating. It makes it easier for me to maintain just one set of physics, and to have cars that adapt to whatever the track I throw at them. I guess that's where not having to fight for every cycle can help.