Added feed for each category in www.blogtal.com
For example:
Technology:
http://www.blogtal.com/categories/technology
Feed for Technology
http://www.blogtal.com/categories/technology/feed
For a better performance purpose, all feed entries (up to 20 latest pings) are loaded from cache. Therefore there is no database query when the feed is loaded. Later, I might need to increase the size of cache to cater more pings for categories.
