Multi-line rules

Currently the following rule is not parsed:

```
background-image: 
        linear-gradient(rgba(0, 255, 0, .7) .1em, transparent .1em),
        linear-gradient(90deg, rgba(0, 255, 0, .7) .1em, transparent .1em);
```


However, rules with `x: v;` should cause strict parsing such that whitespace is irrelevant