feat(subtitle): add artplayer-plugin-libass

docs/index.html

@@ -55,6 +55,10 @@
                                     <a
                                         href="/?libs=./uncompiled/artplayer-plugin-vtt-thumbnail/index.js&example=vtt.thumbnail">artplayer-plugin-vtt-thumbnail</a>
                                 </li>
+                                <li>
+                                    <a
+                                        href="/?libs=./uncompiled/artplayer-plugin-libass/index.js&example=libass">artplayer-plugin-libass</a>
+                                </li>
                             </ul>
                             <ul>
                                 <li class="title">Tools</li>