Sourcemaps

To test, just `ender build` any library, create a `test.html` file that loads the `ender.min.js` file, and run it in Chrome (don't forget to turn on Source Maps in the Inspector options).
I haven't tested it with anything other than small and simple libraries yet, but it should work with any library that consists of one `main` file. I don't think whether or not it has an ender bridge should matter.