Bugfix/reduce large automatic arrays

• Change gfarray into an allocatable array from an automatic array

  Different compilers treat automatic arrays in different ways. For example gfortran puts them on the heap whilst intel puts them on the stack. The gfarray array is likely to be large and can cause problems with intel when there is a limit to the stack size.

  This change avoids the memory requirements associated with gfarray when it is not required.

• Tweak header comment format

Currently just changes gfarray but could reduce peak memory requirements and also avoid some possible stack issues with intel.