Calculate force constants

The subroutine create_force_constants is the bunch of the subroutines treating the forces and the site-point symmetries. These data arrays are rearranged to solve linear equations of a global matrix. Then using the subroutine dgelss of the LAPACK routine, force constants are obtained. The dgelss takes most CPU time and memory area in fropho procedure. Therefore the force constants are written to the FORCE_CONSTANTS file. The calculated force constants contain the effect of the periodic boundary condition.