Combine-csv

This new version add several utilities:
- sas2csv : a conversion utility from SAS .sas7bdat files to plain CSV files
- pivot_csv: a utility doing a 'pivot' transformation, a.k.a a dynamic table in MS Excel.

It also add all current utilities with csv replaced by tsv (combine_tsv, split_tsv, sas2tsv, pivot_tsv) behaving exactly the same but defaulting to TSV files with TAB as default separator.

Adding documentation for split_csv utility in README.md

Adding split_csv: Now you can do the opposite of merging csv, splitting them.