patch 9.0.1827: xxd: no color support

Problem:  xxd: no color support
Solution: Add color support using xxd -R

Add some basic color support for xxd

The hex-value and value are both colored with the same color depending
on the hex-value, e.g.:

    0x00 = white
    0xff = blue
    printable = green
    non-printable = red
    tabs and linebreaks = yellow

Each character needs 11 more bytes to contain color. (Same color in a
row could contain only one overhead but the logic how xxd creates colums
must be then changed.) Size of colored output is increased by factor of
~6. Also grepping the output will break when colors is used.

Flag for color is "-R", because less uses "-R".

Color uses parameters auto,always,never same as less and grep (among
others).

E.g.

xxd -R always $FILE | less -R

Add some screen-tests (that currently on work on linux) to verify the
feature works as expected.

closes: #12131

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Aapo Rantalainen <aapo.rantalainen@gmail.com>
diff --git a/runtime/doc/xxd.1 b/runtime/doc/xxd.1
index 0e7f64f..9ae132b 100644
--- a/runtime/doc/xxd.1
+++ b/runtime/doc/xxd.1
@@ -135,6 +135,12 @@
 particular column layout. Additional whitespace and line breaks are allowed
 anywhere.
 .TP
+.IR \-R " "[WHEN]
+In output the hex-value and the value are both colored with the same color depending on the hex-value. Mostly helping to differentiate printable and non-printable characters.
+.I WHEN
+is
+.BR never ", " always ", or " auto .
+.TP
 .I \-seek offset
 When used after
 .IR \-r :