Add a BeautifulSoup4 parser.

[jeffnappi]

BS4 should provide an extremely robust solution to parsing articles of questionable encoding, etc.

[paul-english]

Note BeatifulSoup4 is required to support Python 3, this has been updated in PR #86

[codelucas]

b015373

[adamramadhan]

how could we use BeatifulSoup4 instead of the default lxml?