adding twitch video embedding

examples:
http://www.shacknews.com/chatty?id=32840425#item_32840425
http://www.shacknews.com/chatty?id=32833602#item_32833602 (with timestamp)
http://www.shacknews.com/chatty?id=32808713#item_32808713 (using b=>a videoId)