Pyopencl for julia and pairwise

I thought hand-written OpenCL might be a good way to get a lower bound on what our compilers are aiming for. I don't think I've written the best possible OpenCL, I look forward to learning e.g. better blocking and codegen techniques from others.

What should I put as license and authors here? Are we going with docstring, comment, or '__license__` var ? What license should I put?