Merge branch 'develop' of https://github.com/1sters/material_design_zh into develop
添加 Switches 章节的所有图片
完成 Switches（未全部完成）

- 两个视频没加
- 还有三句不知道如何翻译
修改进度：Switches
Merge pull request #65 from vincent4j/master

完成 Switches（未全部完成）
添加 Tabs 所有图片
添加视频规范
Merge pull request #66 from IceskYsl/master

添加视频规范
translated buttons chapter in components
Merge remote-tracking branch 'upstream/master'
Merge pull request #68 from vincent4j/master

添加 Tabs 所有图片
Merge pull request #67 from 7heaven/master

translated buttons chapter in components
Merge remote-tracking branch 'upstream/master'
merge from upstream
7heaven 完成 cards
Merge pull request #69 from vincent4j/master

7heaven 完成 cards
add jekyll support
Merge pull request #70 from IceskYsl/master

add jekyll support
Tabs 上半部分
Merge pull request #73 from vincent4j/master

Tabs 上半部分
翻译完成

字体排版（Typography）翻译完成