IOERROR - variable, contains status of last file I/O call.  0 if successful
   see _appendix a_ for example on IOERROR usage

FILEASSIGN - assigns a filename to a file handle
   syntax FILEASSIGN[file f; str filename]

FILEOPEN - opens an existing file for access
   syntax FILEOPEN[file f]

FILECREATE - creates and opens a new file or overwrites an existing one
   syntax FILECREATE[file f]

FILECLOSE - closes an open file
   syntax FILECLOSE[file f]

FILEREAD - reads binary data from a file
   syntax FILEREAD[file f; var target; word count]


FILEWRITE - writes binary data to a file
   syntax FILEWRITE[file f; var target; word count]

FILESEEK - seeks to a position in a file
   syntax FILESEEK[file f; long filepos]

FILEEND - are we at the end of the file?
   syntax FILEEND[file f]:bool

FILESIZE - returns the size of the file
   syntax FILESIZE[file f]:long

FILEPOS - returns the current position in the file
   syntax FILEPOS[file f]:long

FILEREADLN - reads a line of text from a file
   syntax FILEREADLN[file f; str target]

FILEWRITELN - writes a line of text to a file
   syntax FILEWRITELN[file f; str text]


FILEADDTEXT - appends a line of text to a file
   syntax FILEADDTEXT[str f;str text;byte maxlines]