add English version for chapter 7
add Chapter21 code in Go
refines chapter 7 for better readability
Merge pull request #163 from Seamwills/master

Add English version for chapter 7
Merge pull request #162 from gowithqi/master

add Chapter21 code in Go
Update Readme.md
Add a whitespace.
Update 23.0.md
Update 23.0.md
Update 21.0.md
Update 21.0.md
Update 21.0.md
Update 21.0.md
Update 07.0.md
Merge pull request #164 from Frederick-S/master

增强英文版第七章的可读性
update chapter 30
update chapter 29
Update Readme.md
Update Readme.md
Update Readme.md