enableDynamicAck(), Single NOACK, default RT,

- Added new function: enableDynamicAck()  to enable single-write NOACK
payloads (merge closer with gcopeland fork)
- Added single NOACK writes for write(), writeFast(), startWrite() and
startFastWrite()
- powerUp() now checks to see if radio is powered on. No delay if
powered up.
- radio must still be powered up manually if powered down manually
- use setRetries function in begin()
- set CE low on powerDown
- updated readme

nRF24L01.h

@@ -1,24 +1,25 @@
 /*
     Copyright (c) 2007 Stefan Engelke <mbox@stefanengelke.de>
+	Portions Copyright (C) 2011 Greg Copeland
 
-    Permission is hereby granted, free of charge, to any person 
-    obtaining a copy of this software and associated documentation 
-    files (the "Software"), to deal in the Software without 
-    restriction, including without limitation the rights to use, copy, 
-    modify, merge, publish, distribute, sublicense, and/or sell copies 
-    of the Software, and to permit persons to whom the Software is 
+    Permission is hereby granted, free of charge, to any person
+    obtaining a copy of this software and associated documentation
+    files (the "Software"), to deal in the Software without
+    restriction, including without limitation the rights to use, copy,
+    modify, merge, publish, distribute, sublicense, and/or sell copies
+    of the Software, and to permit persons to whom the Software is
     furnished to do so, subject to the following conditions:
 
-    The above copyright notice and this permission notice shall be 
+    The above copyright notice and this permission notice shall be
     included in all copies or substantial portions of the Software.
 
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
-    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 
-    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
-    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT 
-    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
-    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
-    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     DEALINGS IN THE SOFTWARE.
 */
 
@@ -117,6 +118,7 @@
 
 /* P model memory Map */
 #define RPD         0x09
+#define W_TX_PAYLOAD_NO_ACK  0xB0
 
 /* P model bit Mnemonics */
 #define RF_DR_LOW   5