Support for windows

[sthomen]

Make the plugin work when viming on windows. There's an additional commit in this PR that stops the root search when reaching the filesystem root instead of assuming that you always edit under $HOME. It might make sense to make a hybrid solution here, for whatever is hit first ($HOME or the root). I removed it because it had a hard-coded forward slash and I am actually supposed to be working, not working on my tools :-)