Add some fixes and FeedBurner integration

Article links in archives weren't using the SITEURL, so that's fixed now. Also, the Read On button was active all the time, even when the summary length limit was disabled, so I fixed that by checking if the article summary was the same as the article content and only displaying the button when they were different. Finally, I've added FeedBurner support that makes it so that you can still generate a feed for FeedBurner to parse but only link to the FeedBurner feed on the web page.