docs: Use \ instead of \\ in examples (#7286)

Instead of informing the bell character (hex 07), the example was using
an escaped \ followed by x07.

    $ echo \\x07
    \x07
    $ echo \x07

    $ echo \x07 | od -a
    0000000 bel  nl
    0000002
    $

* docs: Use \u instead of \\u

Instead of informing the Unicode character 慡, this example was using an
escaped \ followed by u6161.

    $ echo \\u6161
    \u6161
    $ echo \u6161
    慡

Before:

    $ string escape --style=var 'a1 b2'\\u6161 | string unescape --style=var
    a1 b2\u6161

Now:

    $ string escape --style=var 'a1 b2'\u6161 | string unescape --style=var
    a1 b2慡

doc_src/cmds/string-match.rst

@@ -52,7 +52,7 @@ Match Glob Examples
     >_ string match -i 'a??B' Axxb
     Axxb
 
-    >_ echo 'ok?' | string match '*\\?'
+    >_ echo 'ok?' | string match '*\?'
     ok?
 
     # Note that only the second STRING will match here.