R1 : Encapsulation rules

status: not a lintable rule, covered in preamble

Modules should be split up in a sensible manner to avoid too long Fortran files or too complex modules. One recommendation is to separate the data structures, the operators and the descriptive parameters (including setup if existing). The number of entities in a single module is not limited, but a reasonable total number should be considered always (about 10 to 20 entities ?).