Double-hashing version.

My code of last submission is based on TA's code because I cannot figure out how to invoke double-hashing function. Eventually I found out it was on my class note. Here is my final submission of using double-hashing.
Fixed collision issues.
 Updated my answer of Question part.
 Add some spaces.
 Add spaces.
Made it more logical and added comments.
Merge pull request #18 from JohnneyMing/zhongm2

Zhongm2