Add windows-x86_64 build to liquidfun

[nornagon]

Fixes #524

[nornagon]

Haven't tested this at all, just trying the obvious thing and letting appveyor do the heavy lifting :)

[saudet]

We'll need to add it to the .appveyor.yml file though if we want this to be tested by AppVeyor though...

[nornagon]

lol, whoops. Fixed, hopefully!

[saudet]

BTW, we can speed up the process by temporarily commenting out all other builds from .appveyor.yml and .travis.yml.

[saudet]

BTW2, it is also possible to access the build machine with RDP:
https://www.appveyor.com/docs/how-to/rdp-to-build-worker/
As client http://www.rdesktop.org/ works fine for me on Linux.