Add appveyor.yml

Rakefile

@@ -16,3 +16,6 @@ task :bench do
 end
 
 task :default => :test
+
+desc 'CI test task'
+task :ci => :default

appveyor.yml

@@ -0,0 +1,29 @@
+version: '{build}'
+
+skip_tags: true
+
+environment:
+  matrix:
+    - ruby_version: "193"
+    - ruby_version: "193-x64"
+    - ruby_version: "200"
+    - ruby_version: "200-x64"
+    - ruby_version: "21"
+    - ruby_version: "21-x64"
+
+cache:
+  - vendor/bundle
+
+install:
+  - SET PATH=C:\Ruby%ruby_version%\bin;%PATH%
+  - ruby --version
+  - gem --version
+  - gem install bundler
+  - bundler --version
+  - bundle platform
+  - bundle install --path=vendor/bundle --retry=3 --jobs=3
+
+test_script:
+  - bundle exec rake ci
+
+build: off