Notable changes

• Add ActivityStreams 2.0! New as2 module includes to_as1() and from_as1() functions. Currently supported: articles, notes, replies, likes, reposts, events, RSVPs, tags, attachments.
• Atom:
  • Add new atom_to_activity() function for converting Atom to AS1.
  • Add email field to author, if provided.
• JSON Feed:
  • Raise ValueError on bad (non-dict) input.
• REST API:
  • Add as2 value for format and input. Revise existing ActivityStreams and microformats2 value names to as1, as1-xml, and mf2-json. Old values activitystreams, json, json-mf2, and xml are still accepted, but deprecated.