Updates to CLI / bin utility for node-sass

Merged branch from sjs/add_bin that samsaccone added to get a base for the bin. Updated ability to npm link (assumingly npm install -g would work as well) so that node-sass can be used from the cli.

Also added filesystem output so that compiled scss is written back out and not just displayed on the console.

Usage as such (after npm link):

node-sass sass.scss outfile.css

Where sass.scss is the file to compile, and outfile is the .css file to save the compiled CSS to.

Lots of functionality / stability could be added here for sure!