Support registering webhooks for push updates
It would be great if onionoo would be able to support push updates using webhooks, something similar to pubsubhubbub (https://pubsubhubbub.appspot.com/) which supports push updates for RSS/Atom feeds.
Having push support would make systems like a new Tor Weather much more efficient.
For example, instead of polling onionoo to see if certain nodes are down, it would get a push notification whenever a node's status changes.
It can register for specific nodes or have various other filtering conditions, but that can be discussed later.
Pubsubhubbub supports 2 types of pings (when it has something to notify webhooks that were registered):
Thin - where it only says data was changed but doesn't send the actual data. The receiving party needs pull the relevant data.
Fat - where it sends the actual data that was changed or is relevant for the ping.
This can be implemented as a single system that polls onionoo or as part of onionoo as it knows exactly when certain data changes.