modified fire and integrators to improve performance and adapt to D.Asenjo modified fire, this implementation now performs much more efficiently than the python implementation FireStepBack and yields the same results. However, VelocityVerlet and ForwardEuler integrators are now specific to modifiedfire and cannot be used out of the boc for, say, MD. Therefore consider renaming these integrators to fire_VelocityVerlet and fire_ForwardEuler, the base integrator class remains unchanged however