This was attached to https://gna.org/task/?6847 by Michael Bieri
(https://gna.org/users/michaelbieri), in the zip file calc_modelfree.py_patch.tar.gz
(https://gna.org/support/download.php?file_id=7750).
The new class has been copied and pasted to the bottom of the module, and the comment above the
class was converted into a class docstring.
