陈宇翔增加Chapter_12目录，在目录下增加12.0_Functions_and_Operators文件
Merge pull request #59 from mchenyuxiang/master

陈宇翔增加Chapter_12目录，在目录下增加12.0_Functions_and_Operators文件
Merge branch 'master' of github.com:mysql2cn/manual56