Custom document component
Currently we're using https://github.com/ream/ream/blob/master/packages/ream/app/index.template.html as the template for the whole document, however we can actually use a Vue component for this? Then you can simply create a `src/_document.js` file:

```js
export default {
	functional: true,
	render(h, { props }) {
		const { title, ReamRoot } = props.head
		return (
			<html>
				<head>{title.toComponent()}</head>
				<body>
					<ReamRoot />
				</body>
			</html>
		)
	}
}
```