Add Windows README, modify ping action, fix slashes in paths

On slashes in paths, the [script module](http://docs.ansible.com/script_module.html) does indicate that it's using a local path.

For remote paths, when connecting to Windows hosts only, both forward and back slashes are accepted as path separators, because PowerShell also accepts both.  The examples in the docs may not reflect all possible uses of the module, but [integration tests](https://github.com/ansible/ansible/blob/devel/test/integration/roles/test_win_stat/tasks/main.yml) do account for both cases.