Chapter 2: Minor typographical corrections

Fixed typos of "let's" in "MVC Applied To The Web" section
Chapter 3: Minor corrections and clarification of one paragraph

-Minor spelling, grammatical and punctuation corrections.
-Clarified paragraph that discusses JSON.stringify and toJSON in
"Getters & Setters" section
Merge pull request #323 from jeffjo/gh-pages

Chapters 2 & 3 corrections and clarifications