appveyor.yml: Add support for Windows

This runs the tests on Appveyor CI (basically windows)
so as to keep it from breaking.

Closes #450

appveyor.yml

@@ -0,0 +1,22 @@
+init:
+  - ps: iex (new-object net.webclient).downloadstring('https://get.scoop.sh')
+
+install:
+  - ps: Install-Product node $env:nodejs_version
+  - npm cache clear --force
+  - ps: >-
+      if ($env:nodejs_version -eq "4") {
+        npm install npm@latest-5 -g
+      } else {
+        npm install npm@latest -g
+      }
+  - npm --version
+  - npm install -g bats
+  - scoop install shellcheck
+
+build: false
+
+test_script:
+  - shellcheck -V
+  - bash lint.sh
+  - bash -c 'bats test'