Add appveyor configuration file for continuous integration

.appveyor.yml

@@ -0,0 +1,28 @@
+image:
+  - Visual Studio 2017
+
+environment:
+  matrix:
+    - TOXENV: "py3.5"
+      PY_DIR: C:\Python35-x64
+      PYTHON_VERSION: "3.5"
+      PYTHON_ARCH: "64"
+    - TOXENV: "py3.6"
+      PY_DIR: C:\Python36-x64
+      PYTHON_VERSION: "3.6"
+      PYTHON_ARCH: "64"
+    - TOXENV: "py3.7"
+      PY_DIR: C:\Python37-x64
+      PYTHON_VERSION: "3.7"
+      PYTHON_ARCH: "64"
+
+build: off
+
+init:
+  - cmd: set PATH=%PY_DIR%;%PY_DIR%\Scripts;%PATH%
+
+install:
+  - pip install tox
+
+test_script:
+  - tox