Move tests to another repo about nimpng

[jangko]

Thank you for looking into this. I wasn't aware there are something like this in the compression test data. They were taken from other compression project.
As a compression library developer, we basically only check if the roundtrip compress-decompress works. While the content itself I never look into.

I will remove it.

[jangko]

nimPNG doesn't use external links for test data. maybe they come from other sources?

[exelotl]

The file in question is urls.10k under nimPNG/tests/zcorpus