add configure method to browserify

lib/6to5/browserify.js

@@ -1,19 +1,30 @@
 var transform = require("./transform");
 var through   = require("through");
 
-module.exports = function (filename) {
-  var data = "";
-
-  var write = function (buf) {
-    data += buf;
-  };
-
-  var end = function () {
-    var out = transform(data, { filename: filename });
-    stream.queue(out);
-    stream.queue(null);
-  };
-
-  var stream = through(write, end);
-  return stream;
+var browserify = module.exports = function (filename) {
+  return browserify.configure()(filename);
+};
+
+browserify.configure = function (opts) {
+  opts = opts || {};
+
+  return function (filename) {
+    var data = "";
+
+    var write = function (buf) {
+      data += buf;
+    };
+
+    var end = function () {
+      var opts2 = _.clone(opts);
+      opts2.filename = filename;
+
+      var out = transform(data, opts2);
+      stream.queue(out);
+      stream.queue(null);
+    };
+
+    var stream = through(write, end);
+    return stream;
+  };
 };