mod_pubsub_subscription: New module providing an API for pubsub subscriptions This lets other modules hook events from local or remote XEP-0060 pubsub services. API allows keeping track of items added, removed or if the whole node gets cleared or even deleted. Requested by MattJ.

This module lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
s2s_whitelist = {
    "example.org",
}
```