Fix current directory and issues with paths containing spaces

I was finally go through all the issues and this request is to fix #44 and possible previous issues.

This change aims to fix an issue on all platforms:
* when the scss file is in the same directory as config.rb
* when the paths contain spaces

Sorry about the problems caused, please test it and only merge if it works properly.

So far I have tested this manually with ST2 on Windows, Ubuntu 12.04 and on OS X and with ST3 on OS X