[luatex] adjusting `hyphenate` callback for single function

[Werner LEMBERG]

> They are very old and the syntax has changed in some lua commands
> (and a callback is no longer available), but I found the following
> articles very useful when I was learning how the callbacks work:
> 
> https://tug.org/tugboat/tb31-3/tb99isambert.pdf
> 
> https://tug.org/TUGboat/tb32-1/tb100isambert.pdf

Thanks a lot!  This is indeed very helpful.


    Werner