relax SVN archive

Passed the missing 'data' data structure into write_header().

Fixed the identification of multiple data sets in the write() function.

Another fix for the model_loop() generator.

Fix for the model-free model_loop() generator function.

Removed some unused imports of return_spin_from_index().

Deleted the set_selected_sim() methods, as the base class method is sufficient.

Removed some dud arguments to the model_loop() generator.

Wrote the model-free model_loop() generator method.

Docstring and comment fixes for select_all_sims().

Shifted set_selected_sim() to the base class.