Creating very basic initial procedural demo scene

[TheDuckCow]

PR aiming to address the majority of the scope of this task, currently only partially done so far:

#170

[TheDuckCow]

With the most recent readme page setup, I think this is ready for merging into dev. Some improvements remain, but not the highest priority for right now.

FYI @brickyt that I made a couple more updates in the most recent version - nothing substantially changed since we spoke, but to summarize:

• Added a toggle which is set to true on the RoadLaneAgent to auto visualize the lane its currently on
• Traffic culling had some edge cases which are mostly resolved now; I ended up implementing an 'auto free' feature on RoadLanes to delete all vehicles registered to that lane. For that reason, the player's lane agent now does not register itself to a lane (but it still tracks which lane its on by itself).
• Car spawning is a little more organic now, picking a random position along their initial lane curve
• As mentioned, reduce to just spatials - so no physics being calculated, and no collision meshes.
• Fixed an issue where going backwards wasn't being calculated correctly.

Improvement remaining

• There's a slight flicker of the camera orientation in some cases when going from one lane to the next. This is due (at least partially) to not tracking the "remainder" distance along the next curve when calculating the next point for the look_at. If you were to disable the look at, cars would not rotate but there'd be no flicker, indicating it's only a problem of rotation (for which the camera is hard-parented). This is an improvement I'll be making in RoadLaneAgent eventually, but nothing to worry much about right now.