Notable changes

• Source.original_post_discovery: add new include_reserved_hosts kwarg, defaults to True.
• Facebook:
  • Scraping: handle pictures, videos, link attachments, and text links in timeline/news feed posts.
• Mastodon:
  • Bug fix for get_activities() with fetch_mentions=True: handle notifications with status: null. Maybe happens when a status is deleted?
  • create/preview_create: support bookmarks. (Nothing special happens with them; their content is posted as a normal toot.)
• microformats2:
  • Stop rendering image.displayName as visible text in HTML, since it's already in the <img>'s alt attribute.
  • Add bookmark-of support.
  • Add prefix_image_urls() function.
  • Handle null content in AS1/2 objects.
  • json_to_object bug fix for composite bookmark-of properties.
• Twitter:
  • create/preview: support large videos via async upload. We now pass media_category=tweet_video to the chunked upload INIT stage, and then make blocking STATUS calls until the video is finished processing. (bridgy#1043)
  • create/preview: allow bookmarks. (bridgy#1045)
  • create/preview: allow non-Twitter replies, ie activities that include inReplyTo URLs even if none of them point to a tweet. (bridgy#1063)
  • get_activities: support list ids as well as slugs.
  • Bug fixes for removing t.co links to quoted tweets.
  • Bug fix for multiple instances of the same link in tweet text.
  • get_activities(): raise ValueError on invalid user_id.
• REST API: ported web framework from webapp2 to Flask. No user-visible behavior change expected.