Add support for styled-components

[RabbitShare]

Goals

1. Support for styled-components or emotion

Background

It is hard to use react-email with styled-components. For proper operation, you need to configure plugins for inline styles

Proposal

Update render function api like @anvilco/anvil

const html = '<div>Hello World</div>'
  const css = ''
  return {
    data: {
      html,
      css,
    },
  }

and extract css to inline styles