v0.5.2

Changed

• The :resolve_attachment hook's ctx carries data_dir: dir
  when the loop was started with a :data_dir (a consult: its own
  :data_dir or its loop's; Rho.Loop.context/1 and
  Rho.Session.messages/2's :data_dir likewise), so a host with
  several accounts can tell whose conversation a file belongs to when two
  accounts hold the same session id. Without one, ctx is
  %{session_id: id} as before.