Merge pull request #23 from prife/master

Add more content
Merge pull request #24 from prife/master

add more content for 12-filesystem
actually there are five status of thread
Merge pull request #26 from lgnq/master

actually there are five status of thread
correct the wrong description of parameter
Merge pull request #27 from lgnq/master

correct the wrong description of parameter
fixed a wrong character
Merge pull request #28 from lgnq/master

fixed a wrong character
fixed a wrong spelling of thread state
11-chapter:

Added some content, modify the small part
Merge pull request #30 from caicai07/11-chapter

11-chapter:
Merge pull request #29 from lgnq/master

fixed a wrong spelling of thread state
correct the problem of generated PDF: lack of a newline
modify formate issues in PDF
get pandoc with binary.
Merge pull request #31 from caicai07/11-chapter

correct the problem of generated PDF: lack of a newline
Merge pull request #32 from aozima/pulls

get pandoc with binary.
Update 13-chapter_lwip.md
Update 13-chapter_lwip.md
Update 04-chapter_ipc.md