appveyor.yml: Add support for Windows

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

Closes asdf-vm#450

appveyor.yml

@@ -0,0 +1,14 @@
+init:
+  - ps: iex (new-object net.webclient).downloadstring('https://get.scoop.sh')
+
+install:
+  - git clone --depth 1 https://github.com/sstephenson/bats.git
+  - scoop install shellcheck
+  - set PATH=%PATH%;C:\projects\asdf\bats\bin\
+
+build: false
+
+test_script:
+  - shellcheck -V
+  - bash lint.sh
+  - bash -lc 'bats test'