Python3

This pull request adds compatibility with Python 3. Also adds compatibility with beautifulsoup4, which is the only version of BeautifulSoup that is Python 3 compatible.

Tests pass on Python 2.6, 2.7, 3.2, and 3.3, against Django 1.3.7, 1.4.5, 1.5.1, and 1.6a1, and against BeautifulSoup 3.2.1 and beautifulsoup4 4.2.1.