unify pin naming scheme

examples/SerialTransceiver/SerialTransceiver.ino

@@ -47,7 +47,7 @@ Debug Msg    @<text>;   32 character debug message
 
 #include "HamShield.h"
 
-#define PWM_PIN 3
+#define MIC_PIN 3
 #define RESET_PIN A3
 #define SWITCH_PIN 2
 
@@ -71,8 +71,8 @@ HamShield radio;
 
 void setup() {
   // NOTE: if not using PWM out, it should be held low to avoid tx noise
-  pinMode(PWM_PIN, OUTPUT);
-  digitalWrite(PWM_PIN, LOW);
+  pinMode(MIC_PIN, OUTPUT);
+  digitalWrite(MIC_PIN, LOW);
   
   // prep the switch
   pinMode(SWITCH_PIN, INPUT_PULLUP);