unify pin naming scheme

examples/SignalTest/SignalTest.ino

@@ -25,7 +25,7 @@ char CALLSIGN[] = "1ZZ9ZZ/B";
 #include <HamShield.h>
 #include <PCM.h>
 
-#define PWM_PIN 3
+#define MIC_PIN 3
 #define RESET_PIN A3
 #define SWITCH_PIN 2
 
@@ -90,8 +90,8 @@ const unsigned char dbm[] PROGMEM = {
 
 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);