Use Typescript arrow notation

Found in some parts of your code:

```
var that = this;
image.onload = function () {
that.context.drawImage(image, 32, 32);
};
```

As you are using Typescript would be better to use arrow notation to preserve context:

```
image.onload =()=> {
this.context.drawImage(image, 32, 32);
};
```

Anyway awesome project!!
