Minor fix to REPL output for numbers

Uses # instead of text output. Adds several basic library functions.

src/REPL.hs

@@ -35,5 +35,5 @@ decodeResult tc =
   case ofString tc of
     Right str -> "\"" ++ str ++ "\""
     Left _ -> case ofNumber tc of
-      Right num -> "Number: " ++ show num
+      Right num -> "# " ++ show num
       Left _ -> "Failed to decode number from Tree"