Merge pull request #1 from CocoaChina-editors/master

简单raw版本
Update 17Optional Chaining.md
Merge pull request #55 from Jasonbroker/master

some adjustments
Using Swift with Cocoa and Objective-C chapter 3
修复图片链接
swift functions

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Merge pull request #56 from haolloyin/master

Using Swift with Cocoa and Objective-C 第三章 03Mix and Match