Add support for Source Map Revision 3.
Add support for Source Map Revision 3.

rightisleft/sassc,am11/sassc,saper/sassc,rightisleft/sassc,djam90/sassc,rightisleft/sassc,saper/sassc,am11/sassc,djam90/sassc,saper/sassc,am11/sassc,djam90/sassc