Dev

[XhmikosR]

So, this is not perfect in the sense that the default Windows shell is Powershell, but it should still catch some issues.

I can move the first patch to a separate PR, but this reminds me that the source-map version used here is not the same as in clean-css.

So, regarding Windows:

1. FOO=BAR command does not work. Better use process.env and node foo since Windows don't support shebangs
2. rm and cp don't exist on Windows. Better use native Node fs API

Refs #52

@jakubpawlowicz note that you can push to my branch so that you get this working before merging :)