`normalize()`

Add `normalize()` function. It should mixin [Nicolas Gallagher's normalize.css](https://github.com/necolas/normalize.css).

Depending on the `support-for-*` variables, there are a lot of rules which can be omitted from the original [`normalize.css`](https://github.com/necolas/normalize.css/blob/master/normalize.css).

This function must be used as a mixin from root block:

```stylus
normalize()

html
  body
    background-color: white
```

Maybe some optional arguments could be added to this function to set some initial values –[`font-family`](https://github.com/necolas/normalize.css/blob/master/normalize.css#L10)– or to parametrize some of the rulesets.