Post-processing tool for band unfolding

Band unfolding is done as a post-processing of the SIESTA calculation using the same information as already used to compute Fatbands. Periodicity corresponding to a smaller cell is assumed. It may be an approximate because structural distortions or chemical disordered. The partition of the unit cell into smaller cells in assumed to be diagonal (i.e., the actual supercell used in the calculations is an integer multiple of the smaller unit cell and it is specified a posteriori. "Equivalent atoms" under approximate translations must have the same type of basis, i.e, the same number of orbitals per atom and similar shells.