Log Message:
Update to 5.0. From the changelog:

* Improved MathML support
* Support microformats (rel-tag, rel-enclosure, xfn, hcard)
* Support IRIs
* Allow safe CSS through sanitization
* Allow safe HTML5 through sanitization
* Support SVG
* Support inline XML entity declarations
* Support unescaped quotes and angle brackets in attributes
* Support additional date formats
* Added the request_headers argument to parse()
* Added the response_headers argument to parse()
* Support multiple entry, feed, and source authors
* Officially make Python 2.4 the earliest supported version
* Support Python 3
* Bug fixes, bug fixes, bug fixes