v1.13.0

• teach the plugin how to handle variable interpolation in object keys, e.g.

  css={{
    [theme.breakpoint.sm]: {
      color: 'red'
    } 
  }}

• plugin now emits transient props when replacing css prop calls (cuts down on garbage in the DOM for s-c 5.1+)

• merge withConfig arguments to allow for shouldForwardProp, thanks @ithinkdancan #323

• move injected components to end of file scope, thanks @sfishel18

• Ensure sc- prefix is always added #313, thanks @chalbert