add appveyor.yml

Author: tom-englert

appveyor.yml

@@ -0,0 +1,9 @@
+image: Visual Studio 2017
+configuration: Release
+platform: Any CPU
+#install:
+#- cmd: git submodule update --init --recursive
+build_script:
+- cmd: MSBuild -restore /p:Configuration=Release /verbosity:minimal
+artifacts:
+- path: **/*.nupkg