EveryCSS-nested

Add support for nested rules.

li {
  a, abbr {
    color: blue;
  }

  // `&` usage
  &:before, &:after {
    content: '**';
  }
  
  fo {
    
  }

  // multiple `&` usage
  & > ul > & {
    list-style: circle;

    // deep nesting
    &:first-child {
      list-style: square;
    }
  }

  // back at root level
  @at-root {
    a {
      color: red;
    }
    abbr {
      color: #333;
    }
  }
}