Publish nb

WIP! 

This is a feature that @wandell asked about. Now that we can fire up matlab-only notebooks (e.g. http://nbviewer.ipython.org/github/arokem/ipython-matlabkernel/blob/master/MatlabKernelDemo.ipynb), we can move ahead on this. It's just a matter of some simple text-processing, coupled to IPython's notebook-generating machinery...