Add a directive to apply state

[andershagbard]

Instead of the following:

.card {
  @apply bg-gray-50 hover:bg-gray-100 focus:bg-gray-100;
}

It would be awesome if we could do something similar to:

.card {
  @apply bg-gray-50;

  @state hover, focus {
    @apply bg-gray-100;
  }
}