#5 Support for Publish/Subscribe Hubs

[Dan]

The attached patch includes support for Google's https://pubsubhubbub.appspot.com/ (there's a new Notify Hub button in the Publish window).

Additional (pre-requisite) features:
- hub and self URLs
- feed validation on W3.org (XML Preview window)
- easier GUID for each entry (GUID button when Topic link is empty; see Advanced tab)
- version incremented to 2.1.8.1 (hey Wim, I think your homepage/donate links stopped working soon after 2006)
- other smaller changes

Note: Resource translations are not available for the new features' texts. Also, the patch includes the fix I mentioned in the previous "Fix for Resources Error" patch #2.

[Dan]

Apologies, the previous patch included just a file's changes; see attached.

[Wim Bokkers]

Applied the patch. If you want, I can add you as a developer. As you are aware, this project is not actively maintained anymore.

[Dan]

New patch to 2.1.8:
- added Superfeedr hub support
- fix for select-and-focus new item's title
- changed UI for "Use Link as GUID" button, added GUID button on Advanced tab, added
- date-as-id button on Advanced tab