+ Added ex78

docs/refex/README

@@ -80,4 +80,4 @@ ex74.pp contains an example of the Val function.
 ex75.pp contains an example of the Write(ln) function.
 ex76.pp contains an example of the FillWord function.
 ex77.pp contains an example of the Rename function.
-ex59.pp contains an example of the Ptr function.
+ex78.pp contains an example of the Power function.