Statistical example created by Lynne Williams

WIP: this PR brings in an extended example created by @ljwilliams showing how to do statistics on CSV data using Pandas and statsmodels.  It needs some changes, some code review, and some text editing:

1.  The two MATLAB scripts that generate the data set should be translated into Python.
2.  The data set itself (which is over a megabyte) can then be deleted from the repository and regenerated on demand to save space.
3.  Should we bother to show people how to load CSV data by hand, or just jump straight into the `csv` module, or use something even more sophisticated to load data straight into an array?
4.  There are two versions of the notebook, one showing how to solve the problem using `statsmodels`, one showing how to do it by hand. Which approach should we take?  Or can they be combined, and if so, how?
5.  Editorial cleanup is required on the prose of the lesson, the formatting of titles and exercises, etc. This should be done *after* the core content has been settled.