feat: add danmuku mask plugin for ArtPlayer with initial implementation and documentation

docs/assets/example/danmuku.mask.js

@@ -0,0 +1,19 @@
+// npm i artplayer-plugin-danmuku-mask
+// import artplayerPluginDanmukuMask from 'artplayer-plugin-danmuku-mask';
+
+var art = new Artplayer({
+    container: '.artplayer-app',
+    url: '/assets/sample/video.mp4',
+    autoSize: true,
+    fullscreen: true,
+    fullscreenWeb: true,
+    autoOrientation: true,
+    plugins: [
+        artplayerPluginDanmuku({
+            danmuku: '/assets/sample/danmuku.xml'
+        }),
+        artplayerPluginDanmukuMask({
+            //
+        }),
+    ],
+});