add the in-progress Hello World (and other sm-ssc theming examples).

Themes/HelloWorld/BGAnimations/ScreenTitleMenu background.lua

@@ -0,0 +1,9 @@
+-- this file returns a single quad that represents the background of
+-- ScreenTitleMenu.
+return Def.Quad{
+	-- FullScreen is defined in Themes/_fallback/Scripts/02 Actor.lua in sm-ssc.
+
+	-- colors can either be entered as hex ("#FFFFFFFF") or 0..1 ("1.0,1.0,1.0,1.0")
+	-- where the values are Red, Green, Blue, and Alpha (transparency).
+	InitCommand=cmd(FullScreen;diffuse,color("#fffdf2"));
+};