First steps on converting FeedSub into the pub/sub basis for OStatus communications:

* renamed FeedSub plugin to OStatus
* now setting avatar on subscriptions
* general fixes for subscription
* integrated PuSH hub to handle only user timelines on canonical ID url; sends updates directly
* set $config['feedsub']['nohub'] = true to test w/ foreign feeds that don't have hubs (won't actually receive updates though)
* a few bits of code documentation
* HMAC support for verified distributions (safest if sub setup is on HTTPS)

And a couple core changes:
* minimizing HTML output for exceptions in API requests to aid in debugging
* fix for rel=self link in apitimelineuser when id given

This does not not yet include any of the individual subscription management (Salmon notifications for sub/unsub, etc) nor a nice UI for user subscriptions.
Needs some further cleanup to treat posts as status updates instead of link references.

lib/api.php

@@ -77,6 +77,7 @@ class ApiAction extends Action
 
     function prepare($args)
     {
+        StatusNet::setApi(true); // reduce exception reports to aid in debugging
         parent::prepare($args);
 
         $this->format   = $this->arg('format');