upscaling demo (#1087)
upscaling demo (#1087)

* upscaling demo

This adds a python script to demo the upscaling with a factor of 2, 4
and 8.
libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl