Particles system

It's not totally false but I'm very interested by how many bells and whistles we can add to control in the best condition those sprites :)

Said like this even a physics engine is trivial since it's only "things moving around".

There are interesting things to do with particles system for examples :
- Emiters (Line, area, point,...)
- Orientation (Random, Fixed, Aligned,..)
- Z-order
- Life Time
- Quantity
- Size
- Speed
- Spin
- Forces
- Color/Alpha Life
- Emission (Force, Angle, Arc, Random Motion,...)
- Timed evolution
- Sub-Emiters
- Collisions
- ...