Research and implement a particle effect system.

[boardwalk]

Depends on #12, since animations have the "hooks" that create particle emitters.

The meaning of the fields, particularly particleType, for particle emitters, will need research. My guess is that "parabolic" particle types apply an ax^2 + bx + c equation to the particle. My other guess is that L = local, G = global, V = velocity, A = acceleration, R = rotation in the enumeration. I have no idea how a "non-parabolic" particle behaves, or "swarm", "implode" or "explode".