关于MVVM和RAC的一些拓展阅读
Introduction to MVVM by Ash Furrow
Functional Reactive Programming on iOS by Ash Furrow
MVC, MVVM, FRP, And Building Bridges by Jonathan Penn
MVVM Tutorial with ReactiveCocoa by Colin Eberhardt on the Ray Wenderlich site.
Basic MVVM with ReactiveCocoa by Colin Wheeler
On MVVM, and Architecture Questions by Chris Trott
