Add a skin from Christoballs/Christopher Kelsall

http://pixeljoint.com/pixelart/137461.htm
https://twitter.com/ckelsallpxls/status/1355690030149328900

src/Makefile

@@ -848,7 +848,8 @@ GENERATEDOCOBJ = $(addprefix $(OBJDIR)/,generatedoc.o hotkeys.o keyboard.o)
 SKINS = skin_classic.png skin_modern.png skin_DPaint.png \
         font_Classic.png font_Fun.png font_Fairlight.png \
         font_Melon.png font_DPaint.png \
-        skin_scenish.png font_Seen.png skin_Aurora.png
+        skin_scenish.png font_Seen.png skin_Aurora.png \
+        skin_chrisfx.png
 SKIN_FILES = $(addprefix ../share/grafx2/skins/,$(SKINS))
 SKIN_FILES += $(wildcard ../share/grafx2/skins/unicode_*)
 

src/generatedoc.c

@@ -44,6 +44,7 @@ const char * const skins[] = {
   "DPaint",
   "scenish",
   "Aurora",
+  "chrisfx",
   NULL
 };