Replace all instances of _i4, _i8, r4 and _r8. Note, this affects routine names as well as precision suffixes.

Update OPTION variables to also use standard fortran precision, _int64

Replace declarations using kinds aliases with fortran standard variables. Note, formatting has not been preserved, but it's only cosmetic.

... messages_print_with_emphasis

The use a complex as two doubles required to have the state index running first
in the GPU kernel.

fix indentations
remove trailing white spaces

The routine was not working for integers, causing the code to stop is one tries to initialize all GPU buffers to zero.

Also show the host name. This allows easier identification of ranks and
devices to hosts. Also get rid of the leading zeros in this output.

Batchifying the calculation of the commutator of the position operator and the DFT+U(+V) term. This allows to compute the current fully batchified.

Avoid potential integer overflows when computing the product of
pack_size along its dimensions or with other, potentially large numbers.
Add some more low-level routines to allow calling with i4 and i8
integers.

For large batch sizes, the multiplication of the number of grid points
with the number of states in a batch could overflow. Change the
integers involved to 8-byte.

- protect other calls of phzeev for matrices of size one
- adapt some code style

The main thing was to fix the get_points and set_points methods to allow
for spinor-type wavefunctions. Moreover, some blas calls needed offsets.

Use 8-byte integers throughout the code for global array sizes and
indices. This in principle enables grids with more than 2^31 points.
Large grids have not been tested yet, first I need to make sure
it works for all the tests in the testsuite.

Implement the local potential kernel for complex potentials for all spin
cases and use it in the right place.

With this change, we now use well-defined kind parameters instead of the
non-standard 8.

Also change integer(4) to integer(i4). This makes the code more portable
and adhering to the Fortran standard.