Make use of latest Kryo snapshot which provides Unsafe-based streams

Hi, 

As requested, I provide a pull request for the issue https://github.com/twitter/chill/issues/73
It compiles, but I could not test, because I don't have a local hadoop installation.

It would be nice if someone could give it a try and report any issues that may pop up during testing.
It would be also very interesting to know if there are any performance improvements.

Note: Right now I use UnsafeInput and UnsafeOutput constructors which do not use explicit buffer-size parameter and therefore Kryo will use the default size of 4096. It could be interesting to experiment with different buffer sizes to see how it affects performance.

-Leo