Use Dask for Return Values

[blaiszik]

Dask could solve a lot of the problems in Foundry around unified function return value types and working with datasets that are larger than can fit into memory

https://dask.org

Dask natively has APIs that work with pandas, and clever ways to work with JSON files and directories of input files (e.g., directories of images or csvs)

[blaiszik]

This work can also subsume the JSON-lines functionality in #51

[kjschmidt913]

I think @blaiszik did this sometime within the last few months. Or did we just talk about it? @ascourtas do you remember?