git: use aliases for difftastic instead

.config/git/config

@@ -18,10 +18,6 @@
 	ui = true
 [diff]
 	algorithm = histogram
-[difftool]
-	prompt = false
-[difftool "difft"]
-	cmd = difft "$LOCAL" "$REMOTE"
 [push]
 	default = current
 [branch]
@@ -56,6 +52,9 @@
 	reset-head = remote set-head origin -a
 	head = for-each-ref --format="%(symref:lstrip=-1)" refs/remotes/origin/HEAD
 	sh = "!git switch $(git head)"
+	# show/diff but with difftastic
+	dshow = -c diff.external=difft show --ext-diff
+	ddiff = -c diff.external=difft diff
 
 [include]
 	path = ./config.local