Building Panda3D with MSVC 2015 and Python 3.5/3.6

Some updates, a few new and a few old:

  • Python 3.6.1 is now included.
  • I have posted 32-bit versions of the thirdparty packages.
  • The buildbot now uses VS 2015 to produce the Python 3.5 and 3.6 builds.
  • Panda now compiles successfully on the Express version of VS 2015.
  • Makepanda now also builds assimp on Windows.
  • The thirdparty packages have been built against the v140_xp toolset for Windows XP compatibility.
  • It is no longer necessary to set makepanda to use the Windows 10 SDK; leaving it on the 7.1 SDK will keep the build compatible with Windows XP. You will still need the Windows 10 SDK installed for the Universal CRT, however.