couple evaporation to chemistry

[awbirdsall]

We want to model evaporation as chemistry causes the particle composition to change. Requirements:

• numeric solver for chemistry (0-D)
• appropriate treatment of simultaneous solving of both chemistry and evaporation. Code should be kept separate as much as possible, but full single ODE might need to be assembled at the end, since it's probably either not possible, or not a good idea, to jump back and forth between two ODE solvers at each timestep (i.e., want to avoid "re-entrant" integrators).
• make it easy to define chemistry with some sort of external parameter file(s). Compatibility with evaporation parameter file, and/or chemistry file for a different model, would be good.