Create an HTML element with optional className, innerHTML, and style.

@private
@ignore
function (tagName, opt) {
    var el = document.createElement(tagName);
    if (opt.className) el.className = opt.className;
    if (opt.innerHTML) {
      el.innerHTML = opt.innerHTML;
      var scripts = el.getElementsByTagName('script');
      for (var i = scripts.length; i-- > 0;) {
        scripts[i].parentNode.removeChild(scripts[i]);
      }
    }
    for (var key in opt.style) {
      el.style[key] = opt.style[key];
    }
    return el;
  }