New chapter: Understanding a Request

Just a heads-up: I've written a new chapter for the upcoming 1.2 version of the book. The purpose of this chapter is to help explain how a request is processed in Yesod, start to finish. It is based around the simplified design in Yesod 1.2, and incorporates much of the information I put in the 1.2 blog posts.

Comments, questions and criticism are very welcome! You can view the chapter on the site. If you'd like to submit pull requests, you can see the source on Github.