Windows support

- adds mapping between what node `os` reports for platforms / architectures and what atom-shell is naming its releases. I used package.json for this since that's where the release version was currently being tracked, but not sure if this is the best place for it.

- uses named pipes on Windows, which are close enough to unix sockets for dnode's sake, and avoid all the unpleasantness of TCP sockets (binding to a port, triggering Windows firewall rules, etc)