compute fep examples

• CH4hyd -- free energy of hydration of methane (very simple). FEP and TI methods.

• CH4-CF4 -- free energy difference of transforming methane into perfluoromethane, in water (simple). BAR method.

• CC-CO -- free energy difference of transforming ethane into methanol, in water (more complex). FEP, TI and BAR methods.