Given an array of strings, return all groups of strings that are anagrams.
Note: All inputs will be in lower-case.
http://www.cnblogs.com/AnnieKim/archive/2013/04/25/3041982.html
http://bangbingsyb.blogspot.com/2014/11/leetcode-anagrams.html
原文：http://www.cnblogs.com/grandyang/p/4385822.html