Use tqdm to log progress

[mpariente]

Hi Scott,

Thanks for the scripts and the dataset !
I wonder if you'd consider using tqdm to log the mixture generation progress instead of writing one line per generated mixture.
It'll make the log file much more readable, and that's valuable IMO.

I also added a requirements.txt, but you can remove it if you think it's not useful.

Thanks

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[mpariente]

@googlebot I signed it!

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