Added WIP roundup

[jblondin]

Draft of initial WIP analysis mentioned in #4.

[nevi-me]

Hi @jblondin, happy with what you've written about rust-dataframe, except I don't yet support aggregations.

I've taken a detour to focus on https://github.com/nevi-me/rust-arrow-sql, which aims to abstract away the differences between SQL engines, and create a common SQL <-> Arrow IO thing. That'll enable better SQL support with rust-dataframe.

I'm also working upstream on Arrow to create some of the functions/kernels that'll enable joins and sorts. I can update the WIP analysis when I complete that work.

[jesskfullwood]

Pretty accurate summation of my frames library, nice job! As you have sussed out, it is very similar to agnes in design and has similar advantages and drawbacks, though agnes looks to be somewhat further along in development.