Finished ch12 ch13
Merge pull request #2 from monnand/v1

审校第一至第八章
Merge branch 'v1' of github.com:lifanxi/free-as-in-freedom-zh-cn into v1

Merge monnand's changes
Revise chap 13, 14
Fix compilation problems
Add compare.sh
Merge BG4KKS's review result
Merge BG4KKS review result
Merge branch 'v1' of github.com:lifanxi/free-as-in-freedom-zh-cn into v1