Improve the HelloSIRC example and others

HelloSIRC was not showing ext data;
Other examples needed some changes in the comments.

examples/HelloNEC/HelloNEC.ino

@@ -12,6 +12,7 @@
  */
 
 #define IR_SMALLD_NEC         //1st: define which protocol to use and then,
+//#define IR_SMALLD_NECx
 #include <IRsmallDecoder.h>   //2nd: include the library;
 IRsmallDecoder irDecoder(2);  //3rd: create one decoder object with the correct digital pin;
 irSmallD_t irData;            //4th: declare one decoder data structure;

examples/HelloSIRC/HelloSIRC.ino

@@ -1,14 +1,18 @@
 /* A simple example, using the IRsmallDecoder library, 
  * for testing remote controls that use the Sony SIRC protocol.
  *
- * Note: this example uses an advanced implementation of the SIRC decoder which
+ * 
+ * This example uses an advanced implementation of the SIRC decoder which
  * takes advantage of the fact that most SIRC remotes will send three signal frames
  * every time one key is pressed. That allows the decoder to:
- *  - identify the number of bits of the protocol;      
+ *  - identify the number of bits of the protocol (12, 15 or 20);      
  *  - ignore the two additional repetitions; 
  *  - use the repetitions to check for errors;
  *  - determine if a key is being held. 
  *
+ * If the decoder detects 12 or 15 bits, the ext data member is set to 0.
+ * If it detects a 20-bit code, it will save the extended data in the ext member.
+ * 
  * In this example it's assumed that the IR sensor is connected to digital pin 2 and
  * the pin is usable for external interrupts.
  * 
@@ -25,15 +29,17 @@ irSmallD_t irData;            //4th: declare one decoder data structure;
 void setup() {
   Serial.begin(250000);
   Serial.println("Waiting for a SIRC remote control IR signal...");
-  Serial.println("held\t addr\t cmd");
+  Serial.println("held\taddr\tcmd \tExt");
 }
 
 void loop() {
   if (irDecoder.dataAvailable(irData)) {  //5th: if the decoder has some new data available,
     Serial.print(irData.keyHeld, HEX);    //6th: do something with the data.
-    Serial.print("\t ");
+    Serial.print("   \t");
     Serial.print(irData.addr, HEX);
-    Serial.print("\t ");
-    Serial.println(irData.cmd, HEX);
+    Serial.print("   \t");
+    Serial.print(irData.cmd, HEX);
+    Serial.print("   \t");
+    Serial.println(irData.ext, HEX);
   }
 }

examples/SingleHold/SingleHold.ino

@@ -12,8 +12,8 @@
  *  - Hold the selected keys to turn on/off the built-in LED.
  *    If you keep holding, it won't do anything else.
  *
- * In this example it's assumed that the IR sensor is connected to digital pin 2 and 
- * the pin is usable for external interrupts.
+ * In this example it's assumed that the board has a builtin LED and the IR sensor is 
+ * connected to digital pin 2, which must be usable for external interrupts.
  * 
  * For more information on the boards' usable pins, see the library documentation at:
  * https://github.com/LuisMiCa/IRsmallDecoder