Add support for Windows

[hbyido]

after install on Windows7，type tfstage --help，system said ： it is not a command

[jimfleming]

We rely on a script which probably won't work on Windows. The entry point is defined here: setup.py#L31.

I suspect we'll need a .bat but honestly, I haven't done much Windows development in a while. If you know how to add the equivalent for Windows I welcome a pull request. Otherwise, I'll see if I can add support in the near future.