[BUGFIX] Add fix for source-maps (Fix-Up PR #591)

This fixes some bugs which I unfortunately just discovered now (https://github.com/sass/libsass/pull/591)!

- Remove line-breaks in Base64 encoded string
- Actually embed the source-map json in data-url
- Include original source in sources array

IMO the last one will probably cause some test fails for node sass! /cc @am11, @andrew 
The sources array should contain the initial source too, as there is no other way to get it otherwise. 
IMO I've just added a fix for that so node sass tests pass. After some re-thinking I came to the conclusion that it has to be the way to PR implements it!

Best regards