Another bugfix, improve header documentation a bit.

example/example.ino

@@ -18,6 +18,7 @@ using namespace admux;
 #define BTN2 5
 #define BTN3 6
 #define BTN4 7
+#define BTN5 A0
 
 // pins 8-13 are attached to a 3x3 scanning input matrix. Pins 8-10 are the row pins, 11-13 are the column pins.
 #define MATRIX1 8,11
@@ -68,6 +69,9 @@ void setup() {
   // BUTTON_LATCHED_MOMENTARY lets you turn a momentary pushbutton into a toggle switch.
   // One press will "press and hold" the button. The next press releases the button.
   js.AddButton(BTN4, BUTTON_LATCHED_MOMENTARY);
+
+  // This is a standard PASSTHRU button. It simply mirrors the actual state of the physical button.
+  js.AddButton(BTN5, BUTTON_PASSTHRU);
   
   // One way to get more room for inputs is to use a scan matrix.
   // See http://blog.komar.be/how-to-make-a-keyboard-the-matrix/ for a very detailed discussion of how these work.