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>

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1827,
 /**/
     1826,
 /**/