[新增] 清理TTS缓存(@Luoyacheng)

app/src/main/res/menu/speak_engine.xml

@@ -3,6 +3,12 @@
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto">
 
+    <item
+        android:id="@+id/menu_clear"
+        android:title="@string/clear"
+        android:icon="@drawable/ic_clear_all"
+        app:showAsAction="always" />
+
     <item
         android:id="@+id/menu_add"
         android:icon="@drawable/ic_add"