Make sort(1) utf-compliant and update README

Make it clear that <blank> characters just are spaces or tabs and
not a special group which needs special treatment for wide characters.

Also, and that was the only problem here, correctly calculate the
offset given by the key definitions for the start- and end-characters
using libutf-utility-functions.

Mark the progress in the README and put parentheses around the missing
flags which are insane to implement for no real gain.

README

@@ -69,7 +69,7 @@ The following tools are implemented:
 =*|x sha256sum   .
 =*|x sha512sum   .
 =*|o sleep       .
-     sort        -d, -f, -i
+#    sort        (-d, -f, -i)
 =*|o split       .
 =*|x sponge      .
 #*|o strings     .