Upgrade to Lucene 4.5

Hi!

I've taken the time to update luke to Lucene 4.5 for my own project. Not much needed to be updated. I've detailed a bit the changes in CHANGES.txt.

The only change I'm not so sure about is the one caused by TFIDFSimilarity now using long. Since people may be used to be dealing with byte in the "Field norm" dialog, I've simply taken the first byte out of the long to display. Maybe you have a better idea?

Thanks!