Add AppVeyor configuration

appveyor.yml

@@ -0,0 +1,20 @@
+environment:
+  matrix:
+  - TARGET: x86_64-pc-windows-msvc
+    OTHER_TARGET: i686-pc-windows-msvc
+    MAKE_TARGETS: test-unit-x86_64-pc-windows-msvc
+
+install:
+  - appveyor-retry appveyor DownloadFile https://win.rustup.rs/ -FileName rustup-init.exe
+  - rustup-init.exe -y --default-host x86_64-pc-windows-msvc --default-toolchain stable
+  - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
+  - rustup target add %OTHER_TARGET%
+  - rustc -V
+  - cargo -V
+
+clone_depth: 1
+
+build: false
+
+test_script:
+  - cargo test