Set the correct permissions for create-key on Windows

[thomastaylor312]

With #175 and #115, we have unix support for setting read/write/execute permissions only for the owner of the file. However, it is a little unclear what should be done in Windows. I think the best option is to set the creator/owner to have read/write access and everything else should be denied, but there could be a better option for Windows. Also, as far as I can tell, there is no way to manually pass security options down to the CreateFileA method in the windows API, so this will require importing the windows crate and calling that API manually