naming fix
Use ndarray-stencil - closes #1.

As a consequence, the elements in the outer border of
the grid will always be set to 0. This can be worked
around by using `hi` and `lo` on the grid after
iterating.

Also replacing "ndarray" module with "zeros".
Add border option.
0.2.0
Use ndarray-stencil@0.1.0
0.2.1