Add appveyor script.

appveyor.yml

@@ -0,0 +1,31 @@
+
+environment:
+  matrix:
+    - GENERATOR: "Visual Studio 12 2013 Win64"
+      CONFIG: Debug
+
+    - GENERATOR: "Visual Studio 12 2013 Win64"
+      CONFIG: Release
+
+    - GENERATOR: "Visual Studio 14 2015 Win64"
+      CONFIG: Debug
+
+    - GENERATOR: "Visual Studio 14 2015 Win64"
+      CONFIG: Release
+
+    - GENERATOR: "Visual Studio 12 2013"
+      CONFIG: Debug
+
+    - GENERATOR: "Visual Studio 12 2013"
+      CONFIG: Release
+
+    - GENERATOR: "Visual Studio 14 2015"
+      CONFIG: Debug
+
+    - GENERATOR: "Visual Studio 14 2015"
+      CONFIG: Release
+
+build_script:
+  - git submodule update --init
+  - cmake "-G%GENERATOR%" -H. -B_builds
+  - cmake --build _builds --config "%CONFIG%"