Integrate serial and MPI version. The communicater argument "comm" becomes an optional argument.
Improve interoperability with C by using BIND of fortran 2003/2008.
Modify the name of subroutines
libtetrabz_doubledelta -> libtetrabz_dbldelta
libtetrabz_occstep -> libtetrabz_dblstep
Add and integrate subroutines
Add a routine "libtetrabz_intdos" which compute integrated DOS.
Remove "libtetrabz_polimg" which compute the polarization function at imaginary frequencies, and add rouitne "libtetrabz_polcmlx" which compute the polarization function at complexfrequencies. The new routine has all functions of old routine.
libtetrabz_polimg was not able to compute the polarization function at negative imaginary frequencies. This function is joined into libtetrabz_polcmplx.