doc: typeset long command-line options as literal

Similarly to the previous commit, use backquotes instead of
forward-quotes, for long options.

This was obtained with:

  perl -pi -e "s/'(--[a-z][a-z=<>-]*)'/\`\$1\`/g" *.txt

and manual tweak to remove false positive in ascii-art (o'--o'--o' to
describe rewritten history).

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/diff-generate-patch.txt

@@ -2,7 +2,7 @@ Generating patches with -p
 --------------------------
 
 When "git-diff-index", "git-diff-tree", or "git-diff-files" are run
-with a `-p` option, "git diff" without the '--raw' option, or
+with a `-p` option, "git diff" without the `--raw` option, or
 "git log" with the "-p" option, they
 do not produce the output described above; instead they produce a
 patch file.  You can customize the creation of such patches via the
@@ -118,7 +118,7 @@ index fabadb8,cc95eb0..4866510
 
        diff --combined file
 +
-or like this (when '--cc' option is used):
+or like this (when `--cc` option is used):
 
        diff --cc file