Add support for grunt 0.4.0

As the title says, this adds support for grunt 0.4.0. Some of the required devDependencies aren't up to date in the npm registry so we have to add them by a specific git commit. I also rewrote the `enqueue_ver` task to be compatible with the recent changes to grunt.

Update your global grunt version to 0.4.0 by running this:
```bash
npm uninstall -g grunt
npm install -g grunt-cli@latest
```