test(windows): add appveyor

Author: azu

appveyor.yml

@@ -0,0 +1,22 @@
+# Test against this version of Node.js
+environment:
+  matrix:
+    # node.js
+    - nodejs_version: "6"
+
+# Install scripts. (runs after repo cloning)
+install:
+  # Get the latest stable version of Node.js or io.js
+  - ps: Install-Product node $env:nodejs_version
+  # install modules
+  - npm i -g yarn
+  - yarn install
+
+# Post-install test scripts.
+test_script:
+  # Output useful info for debugging.
+  - node --version
+  - yarn test
+
+# Don't actually build.
+build: off