code: public int[] pieceAvailability() {
          int_vector v = new int_vector();
          th.piece_availability(v);
          return Vectors.int_vector2ints(v);
      }
docs: Returns an array with the availability for each piece in this torrent.
  libtorrent does not keep track of availability for seeds, so if the
  torrent is seeding the availability for all pieces is reported as 0.
  <p>
  The piece availability is the number of peers that we are connected
  that has advertised having a particular piece. This is the information
  that libtorrent uses in order to prefer picking rare pieces.
  
  @return the array with piece availability