Change the example classes UnicodeReader and UnicodeWriter so

Change the example classes UnicodeReader and UnicodeWriter so
that they work with all encodings. For UnicodeReader the real
input stream is wrapped in a line iterator that reencodes the
input to UTF-8. For UnicodeWriter the UTF-8 encoded output is
written to a queue for where it is reencoded to the target
encoding and written to the real output stream.