Fix bug for exporting collapsed elements in the xi3 direction at xi1=0 and xi1=1 in field_io_routines.f90.
Also draft subroutine for cavity volume calculation included, though this portion doesn't need to be merged yet since it is only a skeleton subroutine.
@chrispbradley
Fix bug for exporting collapsed elements in the xi3 direction at xi1=0 and xi1=1 in field_io_routines.f90.
Also draft subroutine for cavity volume calculation included, though this portion doesn't need to be merged yet since it is only a skeleton subroutine.