Add appveyor

appveyor.yml

@@ -0,0 +1,28 @@
+version: 1.0.{build}
+
+branches:
+  only:
+    - master
+
+environment:
+  matrix:
+    - os: Visual Studio 2013
+      GENERATOR_NAME: "Visual Studio 12 2013"
+    - os: Visual Studio 2015
+      GENERATOR_NAME: "Visual Studio 14 2015"
+# TODO: Uncomment when AppVeyor will provide XP toolchain for VS2017
+#    - os: Visual Studio 2017
+#      GENERATOR_NAME: "Visual Studio 15 2017"
+
+clone_folder: c:\projects\xash\hlsdk-xash3d
+
+build:
+  project: INSTALL.vcxproj
+  verbosity: normal
+
+configuration:
+  - Debug
+
+before_build:
+  - git submodule update --init --recursive
+  - cmake -G "%GENERATOR_NAME%"