Add UTF-8 support to 'fold'

[Daimanta]

Like GNU coreutils' 'fold', 'fold' does not really support UTF-8(or any multi-byte encoding). At the moment, characters caught at the wrap place get lost. Nowadays this is considered to be unacceptable and it needs to be remedied.

The following is a sample text that should be supported(but isn't at the moment):

 Τη γλώσσα μου έδωσαν ελληνική
το σπίτι φτωχικό στις αμμουδιές του Ομήρου.
Μονάχη έγνοια η γλώσσα μου στις αμμουδιές του Ομήρου.

από το Άξιον Εστί
του Οδυσσέα Ελύτη