finish function chapter section 1,2,3

Signed-off-by: xiehuc <xiehuc@gmail.com>
finish function chapter section 4

Signed-off-by: xiehuc <xiehuc@gmail.com>
finish function chapter section 5,6,7

Signed-off-by: xiehuc <xiehuc@gmail.com>
Merge pull request #10 from xiehuc/master

finish chapter function