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.
It can download the file just fine but the installer requires cmd to be run as admin so that wouldn't detect it. I could possibly try to write a vbscript to test for permissions but I'm already having trouble getting powershell to run the command correctly for scan.go. Do you want me to implement a test for cmd as admin or should we just leave the big message saying to run as admin?