Split the data processor into a number of parallel workers

[anatoly-scherbakov]

The CSV data processor is right now single-threaded; it processes the lines of incoming data stream one by one, sequentially.

This was acceptable for a proof of concept version, but now we should spawn a number of parallel threads instead. Every thread will work independently of the others.

Every row of the input will be dispatched to those worker threads via channels. When processing is complete, via another channel the output row will be sent to the writer thread.