Add inline documentation for ClusterIterationData refinement control variables

  int lastxi;

  //! \brief ID of the GPU used by one MPI process.

  int proc_device;

  //! \brief Refinement mode selction flag.

  int refinemode;

  //! \brief Maximum number of refinement iterations.

  int maxrefiters;

  //! \brief Required accuracy level.

  double accuracygoal;

  ClusterIterationData(GeometryConfiguration *gconf, ScattererConfiguration *sconf, const mixMPI *mpidata, const int device_count);