Add sourceMap source mapping function.

Author: HairyRabbit

lib/loader.js

@@ -115,7 +115,9 @@ module.exports = function(content, map) {
 			map = result.map;
 			if(map.sources) {
 				map.sources = map.sources.map(function(source) {
-					return source.split("!").pop().replace(/\\/g, '/');
+					const output = source.split("!").pop().replace(/\\/g, '/');
+					if(!query.sourceMapSourcesMapping)  return output
+					return query.sourceMapSourcesMapping(output)
 				}, this);
 				map.sourceRoot = "";
 			}