Pep8 in fvtk.py
NF squeezed_spheres as our new odf plotting function
Changed the name to sphere_funcs
Add the '.fvtk' for consistency (and to make the example easy to run).
Removed mayavi dependencies in the viz module.
Merge pull request #12 from arokem/Garyfallidis-fvtk_spheres

Garyfallidis fvtk spheres
Merge pull request #132 from Garyfallidis/fvtk_spheres

A new fvtk function for visualizing fields of odfs