add 2-19 Nested_Types

add 2-19 Nested_Types
add 3-1 AboutTheLanguageReference

add 3-1 AboutTheLanguageReference
Merge pull request #26 from dabing1022/gh-pages

add 2-19 and 3-1
update the content
Update README.md
Update README.md
add content of ARC
Merge pull request #27 from TimothyYe/develop

add content of ARC
add arc content
bug fix
Merge pull request #29 from TimothyYe/gh-pages

勘误
update arc content
开始“集合类型”章节翻译
Merge branch 'develop' of https://github.com/shinyzhu/the-swift-programming-language-in-chinese into develop