Redefine tone() without ISR

Other minor changes include:
* Enable RTT option for output
  (requires platform.local.txt or boards.local.txt)
* Allow setting compiler optimization
  (requires platform.local.txt or boards.local.txt)

Author: henrygab

cores/nRF5/HardwarePWM.h

@@ -117,6 +117,8 @@ class HardwarePWM
 
 #if CFG_DEBUG
     static void DebugOutput(Stream& logger);
+#else
+    static void inline DebugOutput(Stream& logger) { (void)logger; };
 #endif // CFG_DEBUG
 };