Closure Compilation for JavaScript files.

Still produces warnings, and externs files aren't as complete as they could be. `VowelWorm.Game` works fine, though.

Run thusly:

```bash
npm install
grunt compile # see out/release for output
```

or to compile only the code needed for the demo page, with advanced compilation

```bash
grunt compile-demo # see out/release/vowelworm-demo.min.js
```