some tutorials ported to Python

These are very direct ports from the official java-processing docs (though the object orientation one required a large amount of reworking!), and I've retained the basic structure of the source material: HTML snippets. At some point, the site build script should interpolate these HTML snippets into a template and include them with the rest of the generated HTML files. For now, there's a temporary (static) index file in the Tutorials directory that links to the extant tutorial material.