new_contents: from .abc_lattice import ABCLattice
  from .abc_mesh import ABCMesh
  from .abc_particles import ABCParticles
  from .mesh import Mesh, Point, Element, Edge, Face, Cell
  from .lattice import Lattice, LatticeNode
  from .particles import Particles, Particle, Bond
  
  __all__ = [
      'ABCLattice', 'ABCMesh', 'ABCParticles',
      'Mesh', 'Point', 'Element', 'Edge', 'Face', 'Cell',
      'Lattice', 'LatticeNode',
      'Particles', 'Particle', 'Bond']
  
subject: add easy access to cuds classes