Library contouring and use of derived types in interfaces

[mlange05]

This issue was originally raised by @pmarguinaud in GPU adaptation additions. It pertains to the "Guidelines and recommendations" section. The original in-line comment was:

 * Routine call signatures or interfaces should be designed with care, respecting library                                                                                                                                          
    contouring. Interfaces that are not internal to a component should privilege as much as                                                                                                                                         
    possible native fortran datatypes rather than derived types.                                                                                                                                                                    
                                                                                                                                                                                                                                   
 >>PM: this does not make sense; most modern libraries (eg Atlas) use derived types.<<