Add classes for classical 2d neighborhood.
	
	* oln/core/neighborhood_entry.hh: New.
	* oln/core/abstract/neighborhood.hh: New.
	* oln/core/2d/neighb2d.hh: New.
	* oln/core/gen/neighb.hh: New.
	* oln/core/2d/aliases.hh (neighb2d): New.
	* oln/basics2d.hh: Update.



git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@553 4aad255d-cdde-0310-9447-f3009e2ae8c0