Update examples, minimize code size

- Updated some example files and tests
- Small changes to minimize code size

RF24.h

@@ -50,9 +50,7 @@ private:
   bool wide_band; /* 2Mbs data rate in use? */
   bool p_variant; /* False for RF24L01 and true for RF24L01P */
   uint8_t payload_size; /**< Fixed size of payloads */
-  bool ack_payload_available; /**< Whether there is an ack payload waiting */
   bool dynamic_payloads_enabled; /**< Whether dynamic payloads are enabled. */
-  uint8_t ack_payload_length; /**< Dynamic size of pending ack payload. */
   uint64_t pipe0_reading_address; /**< Last address set on pipe 0 for reading. */
 
 public:
@@ -907,6 +905,8 @@ private:
    * are enabled.  See the datasheet for details.
    */
   void toggle_features(void);
+
+  uint8_t spiTrans(uint8_t cmd);
   /**@}*/
 
 };
@@ -1040,7 +1040,7 @@ private:
  */
 
 /**
- * @example scanner.pde
+ * @example scanner.ino
  *
  * Example to detect interference on the various channels available.
  * This is a good diagnostic tool to check whether you're picking a