Add Dart support

[joseluisq]

It would be great to have Dart support too.

import 'package:test/test.dart'; // external
import 'package:local_package/lib.dart'; // local

void main() {
  // ...
}

[stefanbuck]

Yes! This would be super 👍 Thanks for the idea! Would you like to contribute to make it? The ruby plugin should provide you some hint on how to build it. I'm happy to assist you.

[joseluisq]

I would like to contribute as soon as I get free time again.