Add preliminary arithmetic operator declarations to cpp/array.pxd.
Add preliminary arithmetic operator declarations to cpp/array.pxd.

mwiebe/dynd-python,ContinuumIO/dynd-python,ContinuumIO/dynd-python,insertinterestingnamehere/dynd-python,izaid/dynd-python,insertinterestingnamehere/dynd-python,ContinuumIO/dynd-python,insertinterestingnamehere/dynd-python,izaid/dynd-python,mwiebe/dynd-python,mwiebe/dynd-python,insertinterestingnamehere/dynd-python,ContinuumIO/dynd-python,izaid/dynd-python,mwiebe/dynd-python,izaid/dynd-python