[ADD][GIT] Better diff colors

I like having some colors for the meta-information shown during
diff operations.

Using the `diff-hightlight` script, you can get character-level
highlights of your diffs (just like GitHub and GitLab).

git/.gitconfig

@@ -17,6 +17,23 @@
 [rebase]
     autoSquash = true
     autoStash = true
+[pager]
+    diff = /usr/share/git/diff-highlight/diff-highlight | less
+    log = /usr/share/git/diff-highlight/diff-highlight | less
+    show = /usr/share/git/diff-highlight/diff-highlight | less
+[color "diff"]
+    commit = yellow
+    meta = yellow
+    frag = cyan
+    old = red
+    new = green
+    whitespace = red reverse
+[color "diff-highlight"]
+    oldNormal = red bold
+    oldHighlight = red bold 52
+    newNormal = green bold
+    newhighlight = green bold 22
+
 [user]
     email = bruno.belanyi@epita.fr
     name = Bruno BELANYI