Nick Becker's Timer Assignment

Submitting Nick Becker's timer.py assignment
because you are returning self from the `__exit__ ` method, you are indicating that you will always handle all errors (remember, the boolean value of the return of the `__exit__` method indicates your intention to clean up errors that occur or to let them bubble up to the calling context).  However, you don't actually handle errors here, or accept the proper method parameters.  

Fix this.