Update sending.md

小错误,2.1章节应为1.1章节
Update index.md
Update index.md
Update request-queue.md
Update performance-tips.md
Update performance-tips.md
Merge pull request #124 from Andrwyw/patch-8

performance-tips缺少几段翻译，添加上。
Merge pull request #116 from freshfishyu/patch-1

Update sending.md
Merge pull request #117 from Andrwyw/patch-1

Update creating.md 错别字
Merge pull request #118 from Andrwyw/patch-2

Update files.md 调整一些小地方。
Merge pull request #119 from Andrwyw/patch-3

Update index.md 部分没翻
Merge pull request #120 from Andrwyw/patch-4

Update index.md
Merge pull request #121 from Andrwyw/patch-5

Update request-queue.md
修正错字，并修正翻译

根据原文 "to run your app on the emulator you need to first create an Android Virtual Device (AVD). An AVD is a device configuration for the Android emulator that allows you to model different devices.”。修正了翻译。
Merge pull request #125 from minixalpha/patch-3

修正错字，并修正翻译
增加在线阅读链接
Update receive.md
Merge branch 'patch-9' of https://github.com/Andrwyw/android-training-course-in-chinese