Merge pull request #4 from julycoding/master

Merge master code to my own repo
Update Readme.md
Update Readme.md
Update preface.md
Merge pull request #5 from julycoding/master

Merge master code to my own repo
Add chapter 12~15
Merge pull request #46 from liuyongkang/master

Add chapter 12~15
Update preface.md
Update Readme.md
Update Readme.md
Update preface.md
Update 08.0.md

B* b = new B; will output B no matter "virtual" is added or not.
add chapter 30~31
Update 30.0~31.0.md
Update 30.0~31.0.md
Update 30.0~31.0.md
Update preface.md
Merge pull request #6 from julycoding/master

Merge master code to my own repo
add chapter01 cpp code and improve readability
Merge pull request #1 from julycoding/master

同步作者的更新