douban onebox

Douban.com is a Chinese SNS community for sharing information about books, films, and music. Global rank 280 in alexa. Lots of fun stuff on this site, would be great to have a onebox support for this.

My thoughts during implementation:
Even though I provide douban as a standalone onebox engine. Title and description information are pretty common for many websites, and image url can be retrieved via a [heuristic way](http://stackoverflow.com/questions/3129857/extracting-relevant-image-from-a-web-page). However, currently generic whitelisted engine is ignoring sites that don't support oembed or open graph. And attempt parsing along with those two standards would be helpful if more engines is going to be added.