unify pin naming scheme

examples/HandyTalkie/HandyTalkie.ino

@@ -26,7 +26,7 @@ HamShield radio;
 #define LED_PIN 13
 #define RSSI_REPORT_RATE_MS 5000
 
-#define PWM_PIN 3
+#define MIC_PIN 3
 #define RESET_PIN A3
 #define SWITCH_PIN 2
 
@@ -39,8 +39,8 @@ unsigned long rssi_timeout;
 
 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);