unify pin naming scheme

examples/SSTV/SSTV.ino

@@ -10,7 +10,7 @@
  * 446MHz to receive the image output.
 */
 
-#define PWM_PIN 3
+#define MIC_PIN 3
 #define RESET_PIN A3
 #define SWITCH_PIN 2
 
@@ -28,8 +28,8 @@ int16_t rssi;
 
 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);