minor fixes

- fix erratas
- fix wrong error message
- add 'run' on runnable example
- add explanation about window.onload property corresponding load event
- add comment about window.onstorage property corresponding storage event

1-js/06-advanced-functions/03-closure/7-let-scope/solution.md

@@ -31,7 +31,7 @@ function func() {
   // hence the error
 */!*
 
-  console.log(x); // ReferenceError: Cannot access 'vx before initialization
+  console.log(x); // ReferenceError: Cannot access 'x' before initialization
 
   let x = 2;
 }