Push

A couple of new features in Clojush.

Available as usual from: https://github.com/lspector/Clojush

20110111: - Added zipper stack and functions (thanks to Kyle Harrington for
            draft code, although this was re-written).
          - Added registered-nonrandom function.
          - Modified odd.clj example to use registered-nonrandom.
          - Added examples/dsoar.clj, a version of the "Dirt-Sensing,
            Obstacle-Avoiding Robot" (DSOAR) problem first described in:
              Spector, L. 1996. Simultaneous Evolution of Programs and their
              Control Structures. In Advances in Genetic Programming 2, edited
              by P. Angeline and K. Kinnear, pp. 137-154. Cambridge, MA: MIT Press.
              http://helios.hampshire.edu/lspector/pubs/AiGP2-post-final-e.pdf
            This version was written by Brian Martin in 2010-2011.