Adding complete file trees to a zoo archive

A complete file system can be added to a zoo archive by use of the ``//  create dirs | add complete dirs'' modifier. This modifier is not available in the original zoo program but only in the Atari ST port. It tells zoo the following: If one of the selected files is a directory, recursively⁹ add all its files and subdirectories to the archive.

If the option is not set zoo ignores directories.