Implement second order upwind scheme for particle advection

[Nicholaswogan]

Right now we are using a first order upwind scheme for particles falling. This is very diffusive. We can do better with a second order finite volume upwind scheme.

See Chapter 6 in LeVeque.

One potential issue is that these schemes depend on the size of the timestep. We can get the size of the timestep from CVODE, in the RHS function. I just worry that this will be an issue.

[Nicholaswogan]

I think the timestep size thing is OK. See 10.4 in LeVeque. They say Method of Lines works OK with higher order methods.