Added (corrected) steps data as options

Corrected pull request from #297 since no option to change branch comparison.

> Alternative data assignment to HTML data attributes. Easier (for me) instead do it in the middle of HTML jungle. Also add possibility to provide data from external JS operations. Allowing usage like this

```javascript
// 'slide1' and 'slide2' are step's id

impress.init({
	steps: {
		slide1: { x: -125, y: 50, z: -125, rotate: 90, scale: 0.5 },
		slide2: { x: 105, y: 50, z: -125, rotateX: 45, rotateY: -90, rotateZ: 45 }
	}
});
```
If anything wrong please let me know.