`csv-invert` command line tool

[cmasone-attic]

Takes the output of a CSV file imported as a List of Struct and "inverts" it so that it's now a Struct of Lists.

Example:

List<Struct Row { Base?: String, DOLocationID?: String, }>

becomes

Struct Columnar { base: List, dolocationid: List, }

[cmasone-attic]

Takes about 6 mins to invert ~1GB of imported CSV data here on my lappytop

If we think that's fast enough for right now, then PTAL

[cmasone-attic]

ok, @ehalpern PTAL

[cmasone-attic]

Ok, PTAL