Pulldown attempt

So this uses my [pulldown library](http://github.com/jackfranklin/pulldown) to manage dependencies.

Pulldown uses a simple `.pulldownrc` file that has an array of URLs in, and will download them.   The file looks like this:

```
{
  "destination": "lib",
  "dependencies": [
    "http://requirejs.org/docs/release/2.1.2/minified/require.js",
    "https://raw.github.com/wycats/handlebars.js/master/dist/handlebars.js",
    "http://code.jquery.com/jquery.min.js",
    "https://raw.github.com/requirejs/text/master/text.js"
  ]
}
```

This achieves the following:

- makes `grunt requirejs` work as we'd like it to.
- downloads the JS file to `lib/`
- because it's just one `.pulldownrc` file, it's very easy to delete and replace with package manager of choice
- users can install all the dependencies simply by running `pulldown`.

Please do check this out and have a play with it locally, and also read the pulldown documentation.