Notable changes

Add delete(). Currently includes Twitter and Flickr support.

• Instagram:
  • Make extra HTTP fetch (with cookie) to get individual likes (snarfed/bridgy#840).
  • Update scraping logic to handle feed HTML changes.
  • Link @-mentions in comments as well as photo/video captions.
• GitHub:
  • create/preview_create bug fixes for issues and comments on private repos.
  • Handle HTTP 410 Gone responses from REST API, eg when a repo has been deleted or issues for the repo disabled.
• Twitter:
  • Add delete() and preview_delete() for deleting tweets.
• Flickr:
  • Add delete() and preview_delete() for deleting photos.
• microformats2:
  • Add follow-of support.
  • Only use quotation-of property for quote tweets, not URLs. (#155)
  • If a tag has startIndex/length, it gets linkified in the content, so don't also emit an mf2 child or HTML h-cite for it. (#155
• Atom:
  • Encode &s in author URL and email address too. (Thanks sebsued!)
• AS2:
  • Add Follow support.