Adds appveyor config to ensure build works on windows

[codefromthecrypt]

https://ci.appveyor.com/project/adriancole/zipkin-azure though I suppose there's a way to get this under the project openzipkin? cc @eirslett @openzipkin/devops-tooling

[codefromthecrypt]

green now but test results aren't showing.. maybe there's an integration step to do. https://ci.appveyor.com/project/adriancole/zipkin-azure/build/1.0.5/tests

at any rate this is progress as it shows maven will work on windows

[codefromthecrypt]

once we get this together, we should try on zipkin itself as we've had requests about windows build working (especially zipkin-ui part)

[codefromthecrypt]

merging as otherwise appveyor stains other pull requests. improvements welcome post-merge!