Support 2D/1D periodic boundary conditions

Currently, only 3D periodic boundary conditions are support. To support 2D or 1D periodic boundary conditions the lattice point generation has to be adjusted to account for those cases (all other code is boundary condition agnostic):

https://github.com/awvwgk/simple-dftd3/blob/6393e1ec9102b7604991cf285852b2f8cbf80e56/src/dftd3/cutoff.f90#L53-L78