2.4 demos improvements

[RossNordby]

2.4 comes with pretty major changes, so it would be nice to show them off.

1. Substepping demo could use some updating.
2. Poncho-wearing dancers with a poseable doll driving their motion, with each dancer living its own simulation. Common use case for gamey character cloth.
3. Promote bounciness demo to the DemoSet and make it a bit cleaner and concise.
4. Perhaps a fancier car with squishy tires and a more physical steering mechanism. This might be very annoying to make.
5. Perhaps a chain fountain, because "Chain fountain as a demo would be sick, imo"
6. Perhaps a scissor lift to demonstrate stiffer constraints in a more difficult configuration?

Improving the other basic demos with on-screen descriptions could be nice too. It's not always obvious what the demo is trying to show without looking at the code.

[vpenades]

Not sure if it could be worth adding the "arcade" use case scenario, since it's fairly common.

Such a scene would have to consider:

• objects moving across predefined paths, or driven by non physical dynamics
• collision (overlap) detection, but no collision response (other than event notification)
• fast collision masking (as in, enemy bullets don't need to collision/interect between themselves)

[RossNordby]

That would indeed be nice to have- probably not going to be able to fit it into the 2.4 timeframe, though.

[RossNordby]

Oops, forgot to close this for 2.4's release.