#7952 Update beautifulsoup usage to v4
[#7947] introduced beautifulsoup4, which can be installed side-by-side with beautifulsoup. We should migrate our existing usage of beatifulsoup 3 over to 4.
http://www.crummy.com/software/BeautifulSoup/bs4/doc/#porting-code-to-bs4
Note that when I started using bs4 in [e0e2f0] I had to choose a parser to use. I went with html5lib because it seemed to work better ('html.parser' had some strange </li> behavior in a test). But html5lib spits out html/head/body tags so we'll have to strip those out again.