Adding IPython notebook version of Bechdel test analysis.

Thanks for posting your code for the Bechdel article on GitHub! As you know Brian Keegan has done a nice follow up in this IPython Notebook:

http://nbviewer.ipython.org/github/brianckeegan/Bechdel/blob/master/Bechdel_test.ipynb

Now that the IPython Notebook supports a native R kernel (https://github.com/takluyver/IRkernel), I thought it would be nice to convert your original analysis to a Notebook that can be viewed and shared on http://nbviewer.ipython.org. The Notebook in this PR is basically a simple copy and paste of the R code in this same directory, with a small amount of editing/formatting.