v7.80: Fortran 77 and 90 API reworked

A new way to interface C with Fortran has been worked out as current gfortran ended support for C variable arguments procedures.
The new Fortran API passes all arguments through a set of three tables: one for INTEGER4, one for REAL8 and one for material references.

v7.60

The release v7.6 adds polyhedral meshes handling and helpers functions to customize the library.