Here my modifications to respect the "best-pratices" in Backbone.js :

**Model** - js/models/todo.js

 - remove `initialize` method in Model (useless because `defaults` do already the job)
 - remove `clear` method, we should not change `clear` behavior of Backbone.Model -> http://backbonejs.org/#Model-clear

**Views** - js/views/app.js and js/views/todos.js

 - Call model.destroy() (model.clear(); is not logic)
 - Use this.$el instead of $(this.el) to improve readability and caching

Correct this issue: https://github.com/addyosmani/todomvc/issues/223 with adding `window.app.Todos.on( 'change:completed', this.addAll, this );` and `add` event call now `addAll` method in *js/views/app.js*

Issue related too: https://github.com/addyosmani/todomvc/issues/253