* This also adds separate documentation, header, Fortran wrappers and
  pkg-config file for the cdi-pio part of the library

* This circumvents problems in case not-yet created resources are
  referenced.

* This will allow for later additions of more complex tests.

* Introduces a specialization that fulfills the old interface.

* It is allowed to be NULL when no data is passed on a process.

* Since we don't use MPI_Put this might improve performance.

* This also fixes a previously introduced memory leak.