Improved Extend so that it doesn't bre.ak (N,n) arrays.  It was assume only (N, )
- Cleaned up docstring in Cubic, added examples
Merge branch 'develop' of https://github.com/PMEAL/OpenPNM into develop
Added the ability for Networks to have models
Fixed IO.PNM.load to load any saved Network models
Experimenting with Network models
- Added one that calculates the 'pore_subscripts' (This is actually a hack so that I can regeenrate a cubic network after loading a save)