BF: VTK issue with SetInputData.
RF/PEP8/DOC: Removed unused call to vtkVersion, and clarified a bit the DOCs. Also fixed some line widths as per PEP8.
Merge pull request #26 from ecaruyer/BF_vtk_version_check

BF: VTK issue with SetInputData.
NF: Added a volume_fraction parameter to the isotropic regions.