enhancement - saturn moons

[johndpope]

https://en.wikipedia.org/wiki/Moons_of_Saturn

https://github.com/onekiloparsec/SwiftAA/blob/9aff4344062d5bd32f53024edb8e2ff55a33d2d6/SwiftAA/SaturnRings.swift

[johndpope]

fyi - http://physics.unl.edu/~astrodev/flashdev2/
there's a treasure trove of pretty flash animations here maybe able to port some of these over

[rodericj]

@johndpope yeah great suggestion. I think this could be handled with #41. The logic should be roughly the same and SwiftAA handles them I believe.

tl;dr, I'm down.