add doc to sb::Animation::playing

src/Animation.hpp

@@ -75,7 +75,12 @@ public:
     void pause();
     void unpause();
     void reset();
-    bool playing(bool = true) const;
+
+    /*!
+     * @param include_delay  Specify whether or not to include the delay time in the check
+     * @return               True if the animation is playing
+     */
+    bool playing(bool include_delay = true) const;
 
     /*!
      * Update the timer and check the function's return value to determine whether a new frame of the animation should be produced.