Notable changes

• Moved web site and REST API to granary.io! granary-demo.appspot.com now 301 redirects.
• Twitter:
  • Update the publish character limit to 280. Background.
  • Fix a bug in preview_create that auto-linked @-mentions inside URLs, e.g. Medium posts.
  • Support videos and animated GIFs in get_activities() etc.
• Instagram:
  • Add cookie query param to REST API to allow scraping that logged in user's feed.
• HTML (including Atom content):
  • Render image, video, and audio attachments more often and consistently.
  • Include microformats2 u-photo, u-video, and u-audio classes more often and consistently.
• Atom:
  • Add atom_to_activities() for converting full feed documents.
  • Add to REST API and web UI.
• JSON Feed:
  • Fix bug that omitted title in some cases (#122).