git-diff.txt: backtick quote command text

The modern way to quote commands in the documentation is to use
backticks instead of double-quotes as this renders the text with the
code style. Convert double-quoted command text to backtick-quoted
commands. While we're at it, quote one instance of `^@`.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-diff.txt

@@ -68,13 +68,13 @@ files on disk.
 	This form is to view the results of a merge commit.  The first
 	listed <commit> must be the merge itself; the remaining two or
 	more commits should be its parents.  A convenient way to produce
-	the desired set of revisions is to use the {caret}@ suffix.
+	the desired set of revisions is to use the `^@` suffix.
 	For instance, if `master` names a merge commit, `git diff master
 	master^@` gives the same combined diff as `git show master`.
 
 'git diff' [<options>] <commit>..<commit> [--] [<path>...]::
 
-	This is synonymous to the earlier form (without the "..") for
+	This is synonymous to the earlier form (without the `..`) for
 	viewing the changes between two arbitrary <commit>.  If <commit> on
 	one side is omitted, it will have the same effect as
 	using HEAD instead.
@@ -83,20 +83,20 @@ files on disk.
 
 	This form is to view the changes on the branch containing
 	and up to the second <commit>, starting at a common ancestor
-	of both <commit>.  "git diff A\...B" is equivalent to
-	"git diff $(git merge-base A B) B".  You can omit any one
+	of both <commit>.  `git diff A...B` is equivalent to
+	`git diff $(git merge-base A B) B`.  You can omit any one
 	of <commit>, which has the same effect as using HEAD instead.
 
 Just in case you are doing something exotic, it should be
 noted that all of the <commit> in the above description, except
-in the last two forms that use ".." notations, can be any
+in the last two forms that use `..` notations, can be any
 <tree>.
 
 For a more complete list of ways to spell <commit>, see
 "SPECIFYING REVISIONS" section in linkgit:gitrevisions[7].
 However, "diff" is about comparing two _endpoints_, not ranges,
-and the range notations ("<commit>..<commit>" and
-"<commit>\...<commit>") do not mean a range as defined in the
+and the range notations (`<commit>..<commit>` and
+`<commit>...<commit>`) do not mean a range as defined in the
 "SPECIFYING RANGES" section in linkgit:gitrevisions[7].
 
 'git diff' [<options>] <blob> <blob>::
@@ -144,9 +144,9 @@ $ git diff HEAD       <3>
 +
 <1> Changes in the working tree not yet staged for the next commit.
 <2> Changes between the index and your last commit; what you
-    would be committing if you run "git commit" without "-a" option.
+    would be committing if you run `git commit` without `-a` option.
 <3> Changes in the working tree since your last commit; what you
-    would be committing if you run "git commit -a"
+    would be committing if you run `git commit -a`
 
 Comparing with arbitrary commits::
 +