Once #413 is in, and EXP-code/EXP#136 is addressed, we should:

• Use getAccel() to compute the acceleration instead of getFields (to save on computation)
• Improve C++ exception handling (e.g., evaluating interpolator at a time outside of range)
• Improve speed and benchmark against pyEXP orbit integration
• Hessian
• Pickling, saving, and loading an EXPPotential instance

cc @lgarrison