Setup basic Windows CI

[pietroalbini]

@Eh2406 fixed the Windows build in #267, and it would be nice to have Appveyor checking if the code builds to avoid regressions.

cc @alexcrichton @aidanhs #149

[alexcrichton]

Is crater still heavily docker based? If so that'd narrow the possibilities here a bit and somehow we'd have to build x86_64-pc-windows-gnu libraries on try builds (which we don't currently do, but could in theory do). Otherwise though it may just be getting try builds for Windows working!

[alexcrichton]

Er wait, sorry, this is just CI, in that case you should be able to enable it at any time (in theory any member of rust-lang-nursery can, AppVeyor permissions are a little wonky though)

[pietroalbini]

I'm not actually a member of rust-lang-nursery though, and I still need to get an appveyor config file up.

[pietroalbini]

@alexcrichton I opened a PR (#278) with a basic appveyor.yml, but I'm not admin of the repo/member of rust-lang-nursery. Can you enable AppVeyor for this repo?

[alexcrichton]

Ok I've enabled AppVeyor --