Add appveyor builds.

appveyor.yml

@@ -0,0 +1,22 @@
+environment:
+
+  matrix:
+    - PYTHON: "C:\\Python27"
+    - PYTHON: "C:\\Python36-x64"
+    - PYTHON: "C:\\Python37-x64"
+
+install:
+  - "%PYTHON%\\python.exe -m pip install -r requirements.txt"
+  - "%PYTHON%\\python.exe setup.py develop"
+
+build: off
+
+test_script:
+  # Put your test command here.
+  # If you don't need to build C extensions on 64-bit Python 3.3 or 3.4,
+  # you can remove "build.cmd" from the front of the command, as it's
+  # only needed to support those cases.
+  # Note that you must use the environment variable %PYTHON% to refer to
+  # the interpreter you're using - Appveyor does not do anything special
+  # to put the Python version you want to use on PATH.
+  - "%PYTHON%\\python.exe -m pytest -v"