new_contents: """This package helps you build the topology for CA models.
  
  All ``CellularAutomaton`` subclasses **must** have ``Topology`` class
  declared inside. This class describes:
  
  - ``dimensions``: the number of dimensions your CA model operates on.
  
  - ``lattice``: the type of lattice of your CA board. Built-in lattice
    types are available in ``core.topology.lattice`` module.
  
  - ``neighborhood``: the type of neighborhood for a single
    cell. Built-in neighborhood types are available in
    ``core.topology.neighborhood`` module.
  
  - ``border``: the type of border effect, e.g. how to process off-board
    cells. Built-in border types are available in
    ``core.topology.border`` module.
  
  In example, you can declare the topology for a 2-dimensional
  orthogonal lattice with Moore neighborhood, wrapped to a 3-torus, as
  follows::
  
      class Topology:
  
          dimensions = 2
          lattice = core.OrthogonalLattice()
          neighborhood = core.MooreNeighborhood()
          border = core.TorusBorder()
  
  """
  
subject: Add description of topology package (#23, #27)