Replacement of Cranium section in Fundamentals + Chapter Overviews in Introduction

Added descriptions of the content of each chapter to the end of chapter 1.
Replaced Cranium section of chapter 2 with an example and discussion of how Backbone implements MVC pattern.
Additional wordsmithing and corrections (primarily in chapter 2)

Addy - Here is my proposed replacement to the Cranium section in chapter 2. I tried to borrow from the Todo example to show how Backbone relates to MVC without getting into too much detail about Backbone itself. I also re-worked some of the earlier sections of the chapter to improve flow. I feel like the much of the Implementation Specifics section is redundant with what has been said elsewhere and other parts of it may fit better elsewhere in the book since the chapter is so MVC-focused, but I left it as-is other than some tweaks to make it consistent with the new example.

I also added chapter descriptions at the end of chapter 1. Even though you end the chapter with an overview of what the book covers I felt like it was missing this deeper level and is something I have come to expect in technical books. You should definitely look at these as (having not actually read beyond chapter 3) I may have missed the gist of some of the chapters (I'm not even sure I have all the chapter breaks correct!).