Adds touch/release and pin events to match adafruit/node_mpr121

This is a similar product so it'd be nice if the library could
interoperate on some level.

Author: andrewn

examples/cap1188-events.js

@@ -12,7 +12,19 @@ connectionPromise.then(cap1188 => {
     console.log(evt);
   });
 
-  cap1188.on("reset", function(evt) {
+  cap1188.on("touch", function(pin) {
+    console.log("pin touched: ", pin);
+  });
+
+  cap1188.on("release", function(pin) {
+    console.log("pin released: ", pin);
+  });
+
+  cap1188.on(2, function(touched) {
+    console.log("pin 2 is: ", touched ? "touched" : "released");
+  });
+
+  cap1188.on("reset", function() {
     console.log("reset");
   });
 

lib/CAP1188.js

@@ -86,6 +86,9 @@ class CAP1188 extends EventEmitter {
     for (var i = 0; i < 8; i++) {
       if (currentTouches[i] !== lastTouches[i]) {
         changes.push({ id: i, touched: currentTouches[i] });
+        // Emits touch/release event with pin number
+        this.emit(currentTouches[i] ? "touch" : "release", i);
+        this.emit(i, currentTouches[i]);
       }
     }