work with file-system directories
    
        Create a new directory item that loads in the full tree of the specified
        path, optionally located under some parent path. If parent is "-", then
        loads only the top-level directory, and does not use parent as a path.
        
        
    
    
        Destroy a directory tree and all children it contains.
    
    
        Return directory path
        
    
    
        Return last modification time for directory.
        
    
    
        Return total hierarchy size, in bytes of data contained in all files
        in the directory tree.
        
    
    
        Return directory count
        
    
    
        Returns a sorted list of zfile objects; Each entry in the list is a pointer
        to a zfile_t item already allocated in the zdir tree. Do not destroy the
        original zdir tree until you are done with this list.
        
    
    
        Remove directory, optionally including all files that it contains, at
        all levels. If force is false, will only remove the directory if empty.
        If force is true, will remove all files and all subdirectories.
        
    
    
        Calculate differences between two versions of a directory tree.
        Returns a list of zdir_patch_t patches. Either older or newer may
        be null, indicating the directory is empty/absent. If alias is set,
        generates virtual filename (minus path, plus alias).
        
        
        
        
    
    
        Return full contents of directory as a zdir_patch list.
        
        
    
    
        Load directory cache; returns a hash table containing the SHA-1 digests
        of every file in the tree. The cache is saved between runs in .cache.
        
    
    
        Print contents of directory to open stream
        
        
    
    
        Print contents of directory to stdout
        
    
    
        Create a new zdir_watch actor instance:
            zactor_t *watch = zactor_new (zdir_watch, NULL);
        Destroy zdir_watch instance:
            zactor_destroy (&watch);
        Enable verbose logging of commands and activity:
            zstr_send (watch, "VERBOSE");
        Subscribe to changes to a directory path:
            zsock_send (watch, "ss", "SUBSCRIBE", "directory_path");
        Unsubscribe from changes to a directory path:
            zsock_send (watch, "ss", "UNSUBSCRIBE", "directory_path");
        Receive directory changes:
            zsock_recv (watch, "sp", &path, &patches);
            // Delete the received data.
            free (path);
            zlist_destroy (&patches);