Making it work on Windows

The first 3 commits are required just to get "phr init" + "phr up" to work on windows. I tried to make the changes as unintrusive as possible.

You should really decide whether you want to always use "/" as the directory separator, or always use the DIRECTORY_SEPARATOR constant. Either is good, but mixing them up is what causes problems on windows. For start, I just normalized the separators where needed to make "phr up" work.

In the fourth commit I started fixing tests so they pass on windows. Again, it's linux-specific stuff that fails, see commit messages.

I tested on Travis so you should be OK to merge, but just look over everything in case I messed something up, since I'm not that familiar with the codebase.

Cheers,
Ivan