Merge pull request #4 from evenluo/master

勘误
Merge pull request #6 from evenluo/master

第六章初稿
update
update
Merge pull request #7 from evenluo/master

第十三章初稿
chap 12
merge branch 'master' of https://github.com/AttackOnDobby/iOS-Core-Animation-Advanced-Techniques

aha
chapter 12
Merge remote-tracking branch 'upstream/master'