Fix: txStandBy hang. Updated Transfer example

- txStandBy was hanging if the last of the data timed out. Now clears
the MAX_RT flag if timed out
- Finished updating example file Transfer.ino for demonstrating
half-rate transfers using the FIFO buffers

RF24.cpp

@@ -524,7 +524,7 @@ bool RF24::writeFast( const void* buf, uint8_t len )
 		}
 
   	}
-  			//Start Writing
+		     //Start Writing
 	startWrite(buf,len);
 
 	return 1;
@@ -553,6 +553,10 @@ bool RF24::txStandBy(){
 		ce(LOW);
 		return 1;
 	}
+	if( get_status() & _BV(MAX_RT)){
+		write_register(STATUS,_BV(MAX_RT) );
+	return 0;
+	}
 	return 0;
 }