Update to use latest RTCPeerConnection.

API Changes:

- Changed session.stream to session.streams, as there can be multiple
  remote streams.
- The peerStreamAdded and peerStreamRemoved events now contain two
  parameters: the session that generated the events, and the stream that
  was added/removed.
- Multiple peerStreamRemoved events may be emitted if multiple remote
  streams are active when the session is ended.
0.4.0