Add semi-working fluids
There's something wrong with this..
Add more scene objects and update coordinate system

I switched this to a East-North-Up type system, so that Z is the
vertical axis in world coordinates (x is right, y is forward, z is up).
Start work on 'fires'
Add vector field and updates some things
Improve user interaction
Add heat to fires
Add 3D fluid flow
Add fire starting
Add out-of-bounds checking
Add more user commands
Add textures