Merge pull request #60 from wileam/develop

update 01_The_Basics - Page 60
swift泛型部分翻译
完成
Merge pull request #61 from zengyun-programmer/master

完成
类和结构体完成
Update 21_Protocols.md
Update 21_Protocols.md

校订ing
Update 02_A_Swift_Tour.md

A Swift Tour
Merge remote-tracking branch 'upstream/master' into develop