Some tests for the potential computations
More tests for the simulations
Use Float64 for Array3D instead of Float32.

The memory overhead is not that big
Update REQUIRE file and clean import/using statements
Change internal force and energy units.

The kcal -> kJoule conversion factor is not easy to pickup,
and kJ/mol can be easily converted to accelerations.
Fix the force computation !

Physical results are there for Harmonic potential !!!