AM: use only in internal sub
AM: dont mention unused data_dir
AM: do_final_store(), do_ksmatrix_store() are NOOPs on slaves
AM: convergence is checked in the parallel context

The ugly two-step exit procedure is gone. We still do not trust output
of the convergence checking subs on slave workers.
AM: comments on write_scfcontrol/read_scfcontrol()
AM: diis_fock_matrix(), fixed_fock_matrix() are NOOPs on slaves

A call may still fail it you violate the Fortran standard by passing
unallocated arguments.
AM: use eigen_data_module only where necessary, formatting
AM: whitespace only
AM: rm unused import
AM: whitespace, formatting
AM: rm legacy section around eigen_data_solve()
AM: rm unused eigen_data_solve1()
AM: formatting, comments
AM: comments, formatting
AM: fit_coeff_sndrcv() does handle serial case, rm guards
AM: whitespace, formatting
AM: xc_build() and siblings are called from parallel context

Neither xcfit-, not xcmda-branch was thested though.
AM: rm unused var, receives moved elsewhere
AM: ham_calc_main() is called from a parallel context
AM: witespace, formatting