Add Jigsaw unintended Bias
Note that the tests seem to fail because of a bug in an Exception at the moment, see: https://github.com/huggingface/datasets/pull/2936 for the fix @lhoestq implemented your changes, I think this might be ready for another look. Thanks @lhoestq, implemented the changes, let me know if anything else pops up.
Hi,

Here's a first attempt at this dataset. Would be great if it could be merged relatively quickly as it is needed for Bigscience-related stuff. 

This requires manual download, and I had some trouble generating dummy_data in this setting, so welcoming feedback there.