v27.1.0

• #33: New optional config variables: previewClassName and popupClassName as an array
  of classes, this makes it easier to style the preview:

  {
    "math": {
      "popupClassName": ["myeditor"],
      "previewClassName": ["myeditor"]
    }
  }

  This assures the preview appended to document.body and the popup both are
  accessible via .myeditor.