Building Panda3D with MSVC 2015 and Python 3.5/3.6

@Asimov: all you need to do is extract the thirdparty directory into the Panda source directory, open a command prompt, change to the Panda source directory using “cd”, and type the command at the top of this thread in order to commence the build.

@cbrunner: Sorry, my bad, I guess I had forgotten to push that file. Fixed now.