Log Message:
ocaml-bos: update to 0.2.1.

v0.2.1 2021-10-04 Zagreb

    Require OCaml >= 4.08.
    OS.Dir.create fix function result on existing files. It returned
    non-sensical results. The function now errors as it should be.
    Thanks to Léo Andrès for the report.
    OS.Dir.create fix function returning false instead of true when
    the directory is created with ~path:false. Thanks to Léo Andrès
    for the report and patch.
    OS.File.read support for reading character devices and named
    pipes. Thanks to Rizo Isrof for the patch.