pylab inline mode

fixes #4.

IPython notebook complains about using the `--pylab=inline` parameter and suggests using `%matplotlib` instead but 1) I've never managed to get the latter to work in a docker/vagrant/server context and 2) for our purposes, I think it's good to ensure that inline graphs just always work instead of requiring students to remember to insert a `%matplotlib` cell in each notebook before they do any graphing (and God help you if you import matplotlib before doing that).