Re-organized nRF24L01.h file to place 'P' features in one

location. Changed some bit value interpretation.

Now auto-detects P-vaiants and is queryable. setDataRate now returns a
boolean indicating success or failure of the new data rate
request. The wide_band state indicator has been added and now tracks
the state, including on error fallback. Its now possible to query the
current data rate via getDataRate().

The AA retry duration has been changed to 1500us, which is the lowest
interval allowed when running at 250Kbs, with AA enabled, and 32-byte
packets.

RF24.h

@@ -25,6 +25,7 @@ private:
     uint8_t ce_pin; /**< "Chip Enable" pin, activates the RX or TX role */
     uint8_t csn_pin; /**< SPI Chip select */
     boolean wide_band; /* 2Mbs data rate in use? */
+    boolean p_variant; /* False for RF24L01 and true for RF24L01P */
     uint8_t payload_size; /**< Fixed size of payloads */
     boolean ack_payload_available; /**< Whether there is an ack payload waiting */
     uint8_t ack_payload_length; /**< Dynamic size of pending ack payload. Note: not used. */
@@ -42,6 +43,10 @@ protected:
 
     /**
      * Set chip select pin
+     * Running SPI bus at PI_CLOCK_DIV2 so we don't waist time transferring data
+     * and best of all, we make use of the radio's FIFO buffers. A lower speed
+     * means we're less likely to effectively leverage our FIFOs and pay a higher
+     * AVR runtime cost as toll.
      *
      * @param mode HIGH to take this unit off the SPI bus, LOW to put it on
      */
@@ -416,6 +421,12 @@ public:
      */
     boolean isAckPayloadAvailable(void);
 
+    /**
+     * @return Returns true if the hardware is RF24L01P (or compatible) and false
+     * if its not.
+     */
+    boolean isPVariant(void) const ;
+
     /**
      * Enable or disable auto-acknowlede packets
      *
@@ -471,8 +482,12 @@ public:
     void setPALevel( const rf24_pa_dbm_e level ) const ;
 
     /**
-     * Fetches the current PA level. See setPALevel for
-     * return value definitions.
+     * Fetches the current PA level. 
+     *
+     * @return Returns a value from the rf24_pa_dbm_e enum describing
+     * the current PA setting. Please remember, all values represented
+     * by the enum mnemonics are negative dBm. See setPALevel for
+     * return value descriptions.
      */
     rf24_pa_dbm_e getPALevel( void ) const ;
 
@@ -481,7 +496,16 @@ public:
      *
      * @param speed RF24_250KBPS for 250kbs, RF24_1MBPS for 1Mbps, or RF24_2MBPS for 2Mbps
      */
-    void setDataRate(const rf24_datarate_e speed);
+    boolean setDataRate(const rf24_datarate_e speed);
+
+    /**
+     * Set the transmission data rate
+     *
+     * @return Returns the hardware's currently configured datarate. The value
+     * is one of 250kbs, RF24_1MBPS for 1Mbps, or RF24_2MBPS, as defined in the
+     * rf24_datarate_e enum.
+     */
+    rf24_datarate_e getDataRate( void ) const ;
 
     /**
      * Set the CRC length