Use RSS feed for Ubuntu USN parsing if possible

[sleavitt]

Due to changes in the underlying HTML formatting in the Ubuntu USN homepage, the "current" branch of vFense fails to parse the Ubuntu USNs properly. I noticed that this has been fixed in the "pre-0.8.1-dev" branch, however.

IMO, it would be better to use the RSS feed provided by Ubuntu at http://www.ubuntu.com/usn/rss.xml instead if possible, so that if they make any format changes in the underlying HTML, it isn't as likely to break parsing of Ubuntu USNs.

[linuxdynasty]

I'm in the process of rewriting the parser to no longer use the USN website and use the Ubuntu archives. I will update this issue once it is ready. Thank you for catching this issue.