Implement LZ4 strip and make tools write errors to err instead of out

src/Tools/mkoverlay/src/main.rs

@@ -30,11 +30,11 @@ fn main() {
         Ok(cmd_line) => {
             match run_main(cmd_line) {
                 Ok(_)      => (),
-                Err(error) => println!("{}", error)
+                Err(error) => eprintln!("{}", error)
             }
         },
         Err(error) => {
-            println!("{}", error);
+            eprintln!("{}", error);
         }
     }
 }