Cleaned up code. Using more descriptive variable names. Using BitSet ins...

I was trying to understand how to use SimHash for a project I am involved in, and found your implementation (thanks, btw!). It took me some time to understand what the Main class does, so I changed the variable names for something more representative, cleaned up the code and added comments, so that next people will hopefully understand it a little easier.
Also, I noticed that the previous version was using a StringBuilder to hold a binary string. In order to reduce the memory footprint, I changed it to a BitSet without modifying the original functionality.
As above, there was an array of integers that was holding binary numbers. I also changed it to BitSet.

Thanks.