BUG: Construct `displacement.con` from position and direction

[HaoZeke]

Saddle searches pass saddle which is essentially undefined if pos.con and direction.dat are present without displacement.con. It is of course trivial to generate:

#!/usr/bin/env python
import numpy as np
from ase.io import read, write

init = read("pos.con")
min_01 = read("min1_0Cu.con")

mode = min_01.get_positions() - init.get_positions()
mode /= np.linalg.norm(mode)
displacement = init
displacement.set_positions(displacement.get_positions() +  mode)

write("displacement.con", displacement)
np.savetxt("direction.dat", mode)

But really should be handled within EON.