[sharing] simple jit.gl.pix-based fluid

A jit.gl.pix implementation of the classic, simple fluid simulation.

It's based on the simple equotation: h(x, y, t+1) = damping * (1/2 * (h(x+1, y, t) + h(x-1, y, t) + h(x, y+1, t) + h(x, y-1, t)) - h(x, y, t-1)), the same as utilised in a part of the "pool 3d nurbs example" from standard Jitter examples and the xray.jit.water external (from the XRAY package).