Allow node-sass importers to be passed in options.

index.js

@@ -231,7 +231,18 @@ module.exports = function (content) {
     // indentedSyntax is a boolean flag
     opt.indentedSyntax = Boolean(opt.indentedSyntax);
 
-    opt.importer = getWebpackImporter();
+    // `node-sass`'s importer takes an array of functions. Since `parseQuery` doesn't allow functions,
+    // `opt.importer` has to be a path or array of paths that, once `require`d, return importer functions.
+    opt.importer = []
+        .concat(opt.importer || [])
+        .map(function(path) {
+            return require(path);
+        })
+        .concat(getWebpackImporter());
+
+    // `node-sass` uses `includePaths` to resolve `@import` paths. Append the currently processed file.
+    opt.includePaths = (opt.includePaths || [])
+        .concat(path.dirname(resourcePath));
 
     // start the actual rendering
     if (isSync) {