expose moduleName option - closes #158

doc/usage.md

@@ -113,7 +113,13 @@ to5.transformFile("filename.js", options, function (err, result) {
   // Optionally replace all 6to5 helper declarations with a referenece to this
   // variable. If set to `true` then the default namespace is used "to5Runtime".
   // Default: false
-  runtime: true
+  runtime: true,
+
+  // Optionally declare a function that all import filenames will be piped
+  // through
+  moduleName: function (name) {
+
+  }
 }
 ```