feat: add danmuku plugin documentation and i18n setup guide

- Created a new documentation file for the danmuku plugin with code examples.
- Added comprehensive language settings documentation, including default languages, import instructions, and examples for adding and modifying languages.
- Updated the i18n documentation to reflect changes in language handling and provide clear examples for users.

docs/index.html

@@ -85,10 +85,6 @@
                             <a
                                 href="/?libs=./uncompiled/artplayer-plugin-multiple-subtitles/index.js&example=multiple.subtitles">artplayer-plugin-multiple-subtitles</a>
                         </li>
-                        <li>
-                            <a
-                                href="/?libs=./uncompiled/artplayer-plugin-libass/index.js&example=libass">artplayer-plugin-libass</a>
-                        </li>
                         <li>
                             <a
                                 href="/?libs=./uncompiled/artplayer-plugin-chromecast/index.js&example=chromecast">artplayer-plugin-chromecast</a>