WebSub support for RSS.chat

Previously we were only able to notify via rssCloud. Now we also support WebSub because there are also a fair number of feed readers that only use WebSub. We're using Andrew Shell's rsscloud.io as our WebSub hub , as we have for a long time with rssCloud. Andrew please help us figure out if this is working correctly. The source is in the repo , along with a worknote .