Getting stuff to work in Windows

Unfortunately, at my place of work, we're all on Windows and during my investigation of asset-rack I've hit a lot of hurdles getting it to work :(

My first issue was that the static assets class uses the 'path' module to create URLs which will turn a URL from '/static/blank.txt' in to '\static\blank.txt'.

Then, when I checked out the project on to my windows machine, to make a patch, I couldn't get the tests running. I don't know if you'll like my solution, but I have changed the command in the package.json to the actual mocha command rather than running it through a shell script. But of course, this means that the resolving path wasn't correct when loading fixtures. So that has been changed too.