Issue title: AppVeyor for Windows builds
 Issue body: Travis CI doesn't support Windows builds. However, there is [AppVeyor](https://www.appveyor.com/) which, just like Travis CI, is free for OSS software and provides VMs for Windows. Adding AppVeyor is the next step to 1) test TinySpline on Windows and 2) deploy releases to services like pypi.
 Comments: 
 Comment 0: Fixed with: #106
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