temporary commit.
Add reference for MapReduce new APIs.
Update WordCount source code.
Merge branch 'master' of git.omnilab.sjtu.edu.cn:weijianwen/yet-another-hadoop-tutorial
So what? I just want to merge WordCount.java
Merge branch 'master' of git.omnilab.sjtu.edu.cn:weijianwen/yet-another-hadoop-tutorial