Add more ISPC examples

[gnzlbg]

From stdsimd, the simd crate, and ispc (e.g. aobench).

[gnzlbg]

Mostly fixed in #58 and #59 . We could also add:

• [ ] https://github.com/ispc/ispc/tree/master/examples/volume_rendering
• [x] https://github.com/ispc/ispc/tree/master/examples/stencil
• [ ] https://github.com/ispc/ispc/tree/master/examples/gmres