Windows support for arduino commands!

WinAVR is currently being hosted at https://github.com/hunterboerner/FileMirrors/blob/master/WinAVR-20100110-install.exe until we get a direct link to a file somewhere else. (SourceForge redirect shenanigans mess up the downloader)

Everything else should be self explanatory.
We can start with a message like the current impl, then add a test later.