Property nesting

Hi,

added rule groups. Example:
```sass
body {
    text: {
        align: center;
        transform: uppercase;
    }
}
```
parsed to
```css
body {
    text-align: center; text-transform: uppercase
}
```

_Could not found this feature._ Would be this useful? 

Can also do some code tweaks, if needed, and send a new request.

Cheers.