
  -spec format_error(Reason) -> Chars
                        when
                            Reason ::
                                posix() |
                                badarg | terminated | system_limit |
                                {Line :: integer(),
                                 Mod :: module(),
                                 Term :: term()},
                            Chars :: string().

  Given the error reason returned by any function in this module,
  returns a descriptive string of the error in English.
