Webmention support

Yes, webmentions are a key part of the IndieWeb movement - http://indiewebcamp.com/webmention - and Drupal should certainly support them!

i implemented support or webmention here: https://github.com/sanduhrs/vinculum

It can save the webmentions now, and log activity better, based on sanduhrs implementation, with additions by manarth: https://github.com/HongPong/vinculum

Please check out the new 7.x-2.x branch.

Changing the metas a bit.

Checked out 7.x-2.x-dev and enabled only Vinculum and the Webmention submodule; here are the results from watchdog:

Webmention|192.168.33.1|http://agaric.test/node/add/blog|http://agaric.test/node/add/blog|1||Trying Webmention to %http://agaric.test/blogs/webmention-me from %http://agaric.test/node/262. 
    
php|192.168.33.1|http://agaric.test/node/add/blog|http://agaric.test/node/add/blog|1||Notice: Undefined property: stdClass::$status_message in VinculumWebmentionHandler::send() (line 60 of /vagrant/web/sites/all/modules/vinculum/modules/refback_modules/vinculum_webmention/vinculum_webmention.class.inc).
  
Webmention|192.168.33.1|http://agaric.test/node/add/blog|http://agaric.test/node/add/blog|1||Webmention to http://agaric.test/blogs/webmention-me from http://agaric.test/node/262 got different: -1002 
  
Vinculum|192.168.33.1|http://agaric.test/node/add/blog|http://agaric.test/node/add/blog|1||Ref-backs could not be sent to http://agaric.test/blogs/webmention-me for node Really mention a webmention - no ref-back handler was found.
  
content|192.168.33.1|http://agaric.test/node/add/blog|http://agaric.test/node/add/blog|1|view|blog: added Mention a webmention.

Excited about this module; suggestions for next steps?

added a tiny bit of documentation and gitignore file, trying to get this shaped up a bit...

Webmention is now an official W3C standard as of 2017-01-12:
- https://www.w3.org/TR/webmention/

And; we also now have the following relatively new module, which might become Vinculum's successor if the development does not catch up with reality "soon" - although perhaps these two projects now should merge?
- https://www.drupal.org/project/webmention

Ah thanks @leeteq I didn't know. Perhaps we should work with @sanduhrs and develop the Linkback module instead. It is already registered: https://www.drupal.org/project/linkback . Also I have Microformats module, that could be used: https://www.drupal.org/project/microformats

I can revisit this more next week, and one way or another would love to get this working!

EDIT : I have updated it here https://github.com/HongPong/vinculum-d8 and on this issue #2758041: Linkback 8.x-alpha1 version