Docs: Update radio.sky to use the specced API for shadow roots

sky/examples/radio.sky

 SKY MODULE - radio button and radio button group
 <!-- accessibility handling not implemented yet, pending mojo service -->
 <import src="sky:core" as="sky"/>
 
 <!-- <radio> -->
 <template id="radio-shadow">
  <style>
   :host { width: 1em; height: 1em; border: solid; background: white; }
   :host[checked] { background: black; }
  </style>
 </template>
 <script>
  module.exports = {};
  module.exports.RadioElement = sky.registerElement('radio', class extends Element {
    constructor () {
      this.addEventListener('click', (event) => this.checked = true);
-     this.createShadowTree().appendChild(module.document.findId('radio-shadow').content.cloneNode(true));
+     this.addShadowRoot(new sky.ShadowRoot(module.document.findId('radio-shadow').content.cloneNode(true)));
    }
    get checked () {
      return this.hasAttribute('checked');
    }
    set checked (value) {
      if (value)
        this.setAttribute('checked', '');
      else
        this.removeAttribute('checked');
    }
@@ skipping 13 matching lines @@
 
 <!-- <radiogroup> -->
 <template id="radiogroup-shadow">
  <style>
   :host { padding: 1em; border: thin solid; }
  </style>
 </template>
 <script>
  module.exports.RadioGroupElement = sky.registerElement('radiogroup', class extends Element {
    constructor () {
-     this.createShadowTree().appendChild(module.document.findId('radiogroup-shadow').cloneNode(true));
+     this.addShadowRoot(new sky.ShadowRoot(module.document.findId('radiogroup-shadow').content.cloneNode(true)));
    }
    get value () {
      let children = this.getChildNodes();
      for (let child of children)
        if (child instanceof module.exports.RadioElement)
          if (child.checked)
            return child.name;
      return '';
    }
    set value (name) { 
      let children = this.getChildNodes();
      for (let child of children)
        if (child instanceof module.exports.RadioElement)
          if (child.value == name)
            child.checked = true;
    }
    setChecked(radio) {
      if (!((radio instanceof module.exports.Radio) && radio.parentNode == this))
        throw;
      let children = this.getChildNodes();
      for (let child of children)
        if (child instanceof module.exports.RadioElement)
          if (child != radio)
            child.checked = false;
    }
  });
 </script>