feature request : ability to share derived types through the fortran interface

Currently the PDI fortran interface covers a wide range of data types and sizes, based on the zpp preprocessor and a list containing the types of data that are most commonly used. However this list finds its limits when trying to expose derived types or less frequently used types. The norms introduced in Fortran2008 improved the Fortran/C interoperability thanks to 2 dummy argument generic typing : the assumed type and the assumed shape that are specifically designed for this kind of applications.