void *silc_sftp_fs_memory_add_dir(SilcSFTPFilesystem fs, void *dir,
                                      SilcSFTPFSMemoryPerm perm,
                                      const char *name);

    Adds a new directory to the memory filesystem. Returns the directory
    context that can be used to add for example files to the directory
    or new subdirectories under the directory. The `dir' is the parent
    directory of the directory to be added. If this directory is to be
    added to the root directory the `dir' is NULL.  The `name' is the name
    of the directory. If error occurs this returns NULL. The `perm' will
    indicate the permissions for the directory and they work in POSIX
    style.