move the prelude sources to the prelude directory and add the resource library to cabal

prelude/HTML.gf

@@ -0,0 +1,8 @@
+resource HTML = open Prelude in {
+  oper
+    tag : Str -> Str = \t -> "<" + t + ">" ;
+    endtag : Str -> Str = \t -> tag ("/" + t) ;
+    intag : Str -> Str -> Str = \t,s -> tag t ++ s ++ endtag t ;
+    intagAttr : Str -> Str -> Str -> Str = 
+      \t,a,s -> ("<" + t) ++ (a + ">") ++ s ++ endtag t ;
+}