diff: Add a option for pygments style

kittens/diff/diff.conf

@@ -5,6 +5,10 @@
 # file.abc use a setting of xyz:abc
 syntax_aliases pyj:py recipe:py
 
+# The pygments color scheme to use. See https://help.farbox.com/pygments.html
+# for a list of schemes.
+pygments_style default
+
 # Colors
 foreground            black
 background            white