Netrc windows

Follow up of the discussion on issue https://github.com/jplehmann/coursera/issues/68#issuecomment-15336188, I changed the logic behind the netrc path retrieval (on Windows) to fit most use cases. Tested it on my machine using various settings and it all worked OK.
There are actually two commits since I moved a bit the logger initialization code (otherwise calling logging.info|debug|error before the initialization code breaks all subsequent calls) and separated the commit from the main change. I also included a fairly long comment detailing the absence of standard behaviours for paths on Windows but perhaps such a long comment does not fit your coding style (which I tried to stick to the best I could) ? If so of course, feel free to remove it.
Thanks.
Adrien.