Enable Appveyor

appveyor.ini

@@ -0,0 +1,24 @@
+version: build-{build}-{branch}
+
+environment:
+  matrix:
+    # https://www.appveyor.com/docs/installed-software#python lists available
+    # versions
+    - PYTHON: "C:\\Python27"
+    - PYTHON: "C:\\Python35"
+    - PYTHON: "C:\\Python36"
+    - PYTHON: "C:\\Python37"
+
+init:
+  - "echo %PYTHON%"
+
+install:
+  - "set PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"
+  - python --version
+  - pip install -U virtualenv  # upgrade pip in tox's virtualenvs
+  - pip install tox
+
+build: off
+
+test_script:
+  - tox -e py