Round 1 / go-fil-dataprep

This is a first of its kind streaming tool that does everything related to data preparation, i.e. all that is required until just before deal making. It generates CAR files in a streaming fashion maintaining a fairly small memory footprint without compromising on(in fact in a lot of cases increasing) the throughput. It also provides functionality to split large CAR files into smaller CAR files to ensure that the whole IPLD dag is maintained intact but at the same time CAR file sizes are small enough to fit into a sector.