Version 1.6.4

v1.6.4 [01/06/2021]: Add a function to calculate the hardness.
3D and 2D representations of hardness can be plot by dat2gnu.x and dat2wrl.x.
$ dat2gnu hard: 2D cut of hardness
$ dat2gnu hmhard: 2D Heat map of hardness
$ dat2wrl hard: 3D representations of hardness