sets permissions for a file on S3

        Parameters
        ----------

        target_file : string
            Path to file on S3

        acl : string, optional
            File permissions on S3. Default is public-read

            options:
                - private: Owner gets FULL_CONTROL. No one else has any access rights.
                - public-read: Owners gets FULL_CONTROL and the anonymous principal is granted READ access.
                - public-read-write: Owner gets FULL_CONTROL and the anonymous principal is granted READ and WRITE access.
                - authenticated-read: Owner gets FULL_CONTROL and any principal authenticated as a registered Amazon S3 user is granted READ access


        Examples
        --------
            >>> s3utils.chmod("path/to/file","private")

def chmod(self, target_file, acl='public-read'):
        """
        sets permissions for a file on S3

        Parameters
        ----------

        target_file : string
            Path to file on S3

        acl : string, optional
            File permissions on S3. Default is public-read

            options:
                - private: Owner gets FULL_CONTROL. No one else has any access rights.
                - public-read: Owners gets FULL_CONTROL and the anonymous principal is granted READ access.
                - public-read-write: Owner gets FULL_CONTROL and the anonymous principal is granted READ and WRITE access.
                - authenticated-read: Owner gets FULL_CONTROL and any principal authenticated as a registered Amazon S3 user is granted READ access


        Examples
        --------
            >>> s3utils.chmod("path/to/file","private")


        """
        self.k.key = target_file  # setting the path (key) of file in the container
        self.k.set_acl(acl)  # setting the file permissions
        self.k.close()