IO: Add a dispose method to PCA9685 example, document pulse widths

Developed together with @OlivierLD

java/libraries/io/examples/Servo_I2C_PCA9685/Servo_I2C_PCA9685.pde

@@ -7,8 +7,14 @@ void setup() {
   size(400, 300);
   //printArray(I2C.list());
   servos = new PCA9685("i2c-1", 0x40);
-  servos.attach(0);
-  servos.attach(1);
+
+  // different servo motors will vary in the pulse width they expect
+  // the lines below set the pulse width for 0 degrees to 544 microseconds (μs)
+  //                 and the pulse width for 180 degrees to 2400 microseconds
+  // these values match the defaults of the Servo library on Arduino
+  // but you might need to modify this for your particular servo still
+  servos.attach(0, 544, 2400);
+  servos.attach(1, 544, 2400);
 }
 
 void draw() {
@@ -28,3 +34,8 @@ void draw() {
   y = map(angle, 0, 180, 0, height);
   line(width/2, y, width, y);
 }
+
+void dispose() {
+  servos.detach(0);
+  servos.detach(1);
+}