updated notebook titles and auto-generated the TOC

This PR includes a few changes:
 * The table of contents is now auto-generated. To support this, I created a ``skbiocookbook/__init__.py`` file that contains a function for generating the TOC HTML. 
 * Renamed ``LICENSE`` to ``COPYING.txt``, to match ``scikit-bio``.
 * ~~Added version string in ``skbiocookbook/__init__.py`` (currently ``0.0.0-dev``).~~
 * Renamed notebooks so file names are human-readable titles. This introduces spaces in the file names, but that's better than e.g. trying to title-case after splitting on dashes, which messes up acronyms, class names, etc. 
 * Remove all title cells from the notebooks. These often were different than the file names, so rather than trying to sync the notebook names in multiple places we now just use the file name as the definitive name for each notebook. 

[Rendered notebook available here](http://nbviewer.ipython.org/github/gregcaporaso/scikit-bio-cookbook/blob/toc-updates/Index.ipynb).