Merge pull request #38 from JohnRiv/backbone

Updating Backbone.js & Underscore.js source files & a couple tweaks to the Exercise 1 slides & instructions
Fix Backbone View/Model Events code sample

There is a bug in old code: after each book added render method called that append all old books and plus one new. So after each addition we duplicate all old books.
Merge pull request #39 from dmytroyarmak/master

Fix Backbone View/Model Events code sample