Find a way to deal with UTF-8 with old `awk` versions

[phyver]

The script box.awk displays a frame around a text file. Some versions of awk (for example the one on macOS or BSD) do not return the correct length on UTF-8 string:

$ awk 'BEGIN {print length("hééé")}'
4
$ mawk 'BEGIN {print length("hééé")}' 
7

When the text file contains non-ASCII characters, the right border isn't aligned properly. One way to deal with that could be to try using iconv (POSIX, but not installed everywhere by default) : UTF-8 -> ISO-something -> box -> UTF-8.

Doing that would make it possible to completely remove the box8.py script.

A similar thing could be used when the detected locale is not UTF-8.

[phyver]

9d05c95 should correct that:
if a version of awk doesn't get the length of UTF-8 right, and if iconv is found, box.sh converts the text to ISO-8859-15 (an 8 bit encoding of european characters), pass it to box.awk, and pass the result to iconv again to get back UTF-8.