Consider support for parallel processing

[liquidaty]

Variants:

• generate/use index
• naive 1-pass chunking with explicit flag (e.g. --unquoted)
• 1-pass chunking using algorithmic resolution to ambiguity (see e.g. https://www.microsoft.com/en-us/research/uploads/prod/2019/04/chunker-sigmod19.pdf)

While indexing is slower than other methods, the time to index is likely negligible compared to the time required for meaningful processing, whatever that may be.