Unicode support in io Forge package

[Andrew Janke]

Hi, Octave and io maintainers,

I'm confused by the Unicode support in the io package. In particular, 
the functions unicode2utf8 and utf82unicode, and the "encode_utf" 
options in some of the ods/xls read/write functions.

What is the encoding that utf82unicode/unicode2utf8 are calling 
"unicode" here? It looks like it's doing a single-byte encoding, 
treating each byte as an unsigned int 0-255, and treating those 0-255 
values directly as Unicode code point values. That's not any of the 
standard Unicode encodings. (But I think it is exactly the same as 
Latin-1/ISO 8859-1.)

As I understand it, since about Octave 4.4, Octave's internal encoding 
(that is, how it interprets Octave char arrays) is either UTF-8 or an 
opaque array of bytes; it's never in the "system code page" or some 
other locale-specific encoding.

Is this UTF-8 support in io still relevant/correct? Maybe it should be 
deprecated or renamed/removed? Since Octave now supports UTF-8, I think 
you'd want to just leave UTF-8 text as is in all cases.

Cheers,
Andrew