message: network.Socket: Make all sockets `Printable`.
diff: @@ -27,6 +27,7 @@ namespace elle
  /// - close
  class Socket
  : public elle::IOStream
  + , public elle::Printable
  {
  /*------.
  | Types |
  @@ -169,7 +170,6 @@ namespace elle
  typename EndPoint_ = typename AsioSocket_::endpoint_type>
  class PlainSocket
  : public Socket
  - , public elle::Printable
  {
  /*--------.
  | Types. |
  