Option to keep .zip not csv

[mdavis-xyz]

I want to keep original data, to avoid re-downloading it (my internet is slow). I don't want to keep the raw CSVs because they're too big. So I'd prefer keeping the raw zips.

I can try writing a pull request for this eventually. I'm just raising these feature requests so that I can keep track of the changes I want to make.

[mdavis-xyz]

This could also help solve #16