Merge pull request #34 from prife/master

fix 11-chapter_finsh format
Merge pull request #37 from prife/master

fix errors
Merge pull request #38 from prife/master

add content to 08-app module
Update 13-chapter_lwip.md
fix spell errors, fixed #40.
fix spell errors, fixed #41.
fix spell errors, fixed #42.
Merge pull request #43 from aozima/pulls

fix spell errors, fixed #40.
Update 03-chapter_timer.md

错别字
Merge pull request #44 from roamboy/master

Update 03-chapter_timer.md
finsh: add msh description