RAC学习资料
http://limboy.me/
http://tech.meituan.com/tag/ReactiveCocoa
https://www.coursera.org/course/reactive
http://blog.leichunfeng.com/blog/2015/11/08/functor-applicative-and-monad/
http://www.raywenderlich.com/62699/reactivecocoa-tutorial-pt1、
http://www.raywenderlich.com/62796/reactivecocoa-tutorial-pt2、
http://www.raywenderlich.com/74106/mvvm-tutorial-with-reactivecocoa-part-1、
http://www.raywenderlich.com/74131/mvvm-tutorial-with-reactivecocoa-part-2。