Adds ocaml library “csv”

This is a pure OCaml library to read and write CSV files, including all
extensions used by Excel — eg. quotes, newlines, 8 bit
characters in fields, "0 etc.

Homepage: https://forge.ocamlcore.org/projects/csv/
Merge pull request #3632 from vbgl/ocaml-csv

Adds ocaml library “csv”