This module provides functions for reading file directories from
disks, disk like devices, and possihly tapes.

At the beginning of the program use the directives

  #include <fileio.h02>
  #include <dirent.h02>

The following structures are defined:
  
  struct dirhdr dh;     Directory Header. At a minumum this will contain
                        the member name[128], which is the directory
                        name or disk label.

  struct dirent de;     Directory Entry. At a minumum this will contain
                        the member name[128], which is the filename.

The following functions are defined:

   f,e = opndir(d,&n);  Open directory named n with options d, returning
                        channel number f and error code e.
                        
                        The options byte d consists of the device number
                        and drive numbet combined ny the | operator.
                        
                        If the return channel number is 0, the directory
                        was not opened.

   e = clsdir(f);       Close directory opened on channel f, returning 
                        error code e.
                        
   n,e = rdhdr(f,&dh);  Read directory header into dirhdr structure dh,
                        returning the length of the header in n and error 
                        code in e. If the header length is 0, then the
                        directory does not have a header, or there was
                        and error during the read.
                            
                        This should be called after opndir() and before 
                        the first rddir()
   
   n,e = rddir(f,&de);  Read directory entry into dirent structure de,
                        returning the length of the entry in n and error 
                        code in e. If the entry length is 0, then the
                        end of the directory was reached or there was
                        an error during the read.

Note: This library expects the following functions to be defined:

  fsaddr();                 Set File Address
  fsname();                 Set Filename