Create Hero Engine constructor

Something like:

```js
new HeroEngine({

  // the Tiled json file containing your game
  level: "assets/level.json",

  // optional, customize the configurations passed into Phaser.Game()
  phaser: {
    type: Phaser.AUTO,
    width: 800,
    height: 600,
    backgroundColor: '#2d2d2d',
    parent: 'phaser-example',
  }
});
```