Add appveyor for automated Win testing

appveyor.yml

@@ -0,0 +1,13 @@
+os: Visual Studio 2017
+environment:
+  matrix:
+  - TARGET: x86_64-pc-windows-msvc
+install:
+  - appveyor DownloadFile https://win.rustup.rs/ -FileName rustup-init.exe
+  - rustup-init.exe -yv --default-host %target%
+  - set PATH=%PATH%;%USERPROFILE%\.cargo\bin
+  - rustc -vV
+  - cargo -vV
+  - rustup component add rustfmt
+build: false
+test_script: test-all.bat