Styled System support

## Describe the feature
https://github.com/styled-system/styled-system

Styled System is getting a lot of attention, and currently works with Emotion and Styled Components. Something to keep in mind for future dev.

```jsx
import { styled } from "linaria/react";
import space from "@styled-system/space";

export const Container = styled.div`
${space}
display: flex;
`;

```

This currently results in `--c155nh7h-0: [object Object];` on the element (I am guessing ${space} isn't being executed as a function, like it does in Emotion/SC