Distinguish between path to model files and path to data files in setup

[jodemaey]

To be more specific, currently, the path_name argument to the BifurcationDiagram object is only concerned with where to save the AUTO :

b = BifurcationDiagram('...', path_name='...')

and AUTO² output files, while the AUTO Fortran and configuration files have to be stored at the same place as the scripts or notebooks that use AUTO². The current path_name argument could become save_path, and path_name (or maybe model_path) would become used to determined where the Fortran and config file are stored. This would be useful in the framework of big projects with multiple folders and models.

Technically, it would be done with a context manager for each path. It remains to be checked if it would work with AUTO Python bindings.

Suggested by @nicolasdero .

[jodemaey]

If this is not possible, then it should be made clearer in the documentation.