Add Appveyor configuration file for Windows CI.

appveyor.yml

@@ -0,0 +1,22 @@
+build: off
+
+before_test:
+# http://help.appveyor.com/discussions/problems/6312-curl-command-not-found
+- set PATH=C:\Program Files\Git\mingw64\bin;C:\Qt\5.10.1\mingw53_32\bin;%PATH%
+
+- curl -sS -ostack.zip -L --insecure http://www.stackage.org/stack/windows-i386
+- 7z x stack.zip stack.exe
+
+clone_folder: "c:\\stack"
+environment:
+  global:
+    STACK_ROOT: "c:\\sr"
+
+test_script:
+- 'echo resolver: lts-11.1 >stack.yaml'
+- 'echo packages: >>stack.yaml'
+- 'echo - . >>stack.yaml'
+- stack setup > nul
+# The ugly echo "" hack is to avoid complaints about 0 being an invalid file
+# descriptor
+- echo "" | stack --no-terminal test --jobs 1