Galaxy 10 datasets

[bkmgit]

Consider adding

• https://astronn.readthedocs.io/en/latest/galaxy10sdss.html 200MB
• https://astronn.readthedocs.io/en/latest/galaxy10.html 2.5GB

Code should be similar to https://github.com/red-data-tools/red-datasets/blob/master/lib/datasets/cifar.rb