Fix: Due write() issues.

Found that Due would send multiple payloads or fail in writing in some
cases. Change ensures single-payload transmission using write().
- Updated pingpair_dyn.ino example sketch to conform with available()
changes
- Slight doc update

RF24.cpp

@@ -579,15 +579,13 @@ void RF24::powerUp(void)
 bool RF24::write( const void* buf, uint8_t len )
 {
 	//Start Writing
-    startFastWrite(buf,len);
+    startWrite(buf,len);
 
 	//Wait until complete or failed
 	//ACK payloads that are handled improperly will cause this to hang
 	//If autoAck is ON, a payload has to be written prior to reading a payload, else write after reading a payload
 	while( ! ( get_status()  & ( _BV(TX_DS) | _BV(MAX_RT) ))) { }
 
-	ce(LOW); //Set the radio back to STANDBY-I mode since we can only fill one buffer at a time using this method, and tx is complete
-
 	uint8_t status = write_register(STATUS,_BV(RX_DR) | _BV(TX_DS) | _BV(MAX_RT) );
 
   //Max retries exceeded