Add 88 Soils beta diversity recipe

Fixes #13. @gregcaporaso can you please review? Link to rendered notebook [here](http://nbviewer.ipython.org/github/jairideout/scikit-bio-cookbook/blob/issue-13/Exploring%20beta%20diversity%20in%20the%2088%20Soils%20dataset%20with%20scikit-bio.ipynb).