Redefine F() as no-op

megaAVR 0-series have a unified address space so forcing a const string in flash just increases flash occupation with no benefit on RAM usage.
Fixes #53

Author: MCUdude

Diff for: cores/arduino/Arduino.h

@@ -26,6 +26,9 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 
+#undef F
+#define F(str) (str)
+
 #ifdef __cplusplus
 extern "C"{
 #endif