Added Lab 2 (Web Scraping)

For some reason, Lab 2 (Web Scraping) was missing from the repo. It was surprisingly difficult to find through Google, but I tracked it down to this [gist](https://gist.github.com/thouis/6541913). I downloaded the gist, put it in the lab2 folder in lab/, and updated the Lab section in the README to point to the [online version](http://nbviewer.ipython.org/urls/gist.github.com/thouis/6541913/raw/3986b40ca96007ab3b6ff2587adefb0edc5983c1/Lab_2_A_Live_Ray_Final.ipynb).