Merge pull request #27 from jinglong/master

fix some typos in chapter12
Update source/chapter_02.rst
Update source/chapter_02.rst
Update source/chapter_02.rst
Update source/chapter_02.rst
Update source/chapter_06.rst

更新nginx只用边沿触发的错误描述
1, add content for chapter 12\n 2, delete unnecessary *.pyc files in exts
delete unnecessary *.pyc files in exts
add .gitignore