migrate Vowpal Wabbit to run on Visual Studio 2013 and Windows 8.1

I've done some work to make Vowpal Wabbit run on Visual Studio 2013
I moved to Boost 1.56.0 since earlier versions required some ugly patching to Boost
Zlib 1.2.8 still needs  some minor fixes which I've added to a patch
I also fixed some minor bugs in the VW solution.

The details are appended to the README.windows.txt