Compliance of code to F2003 standard plus further cleaning
* Removal of non-f2003 constructs
-- non-standard intrinsics: dcmplx, dconjg, dreal, etc -- non-standard extensions for POSIX calls (chdir, system, etc) These are now implemented using the 'iso_c_binding' module. -- non-standard variable declarations (real*8, etc)
* Avoid use of 'mpif.h' in MPI compilation. Replace by 'use mpi'
* Avoid compiler checks for reallocation on assignment: whole array assignments now use array-section syntax in the left-hand side.
* Fix of a number of potential interface problems
* Some dead code has been removed
* The code should now compile with only 'benign' warnings with the gfortran flags: