Open, close and toggle events

You can now trigger a open, close or toggle event on any collapsed collection, or a specific section:

```js
$("#demo").trigger("open") // open all sections
$("#demo").trigger("close") // close all sections
$("#demo h2 a").last().trigger("toggle") // toggle last section
```

This commit contains a few backwards incompatible changes:
The event's being triggered from the plugin is now "opened" and "closed" as opposed to "open" and "close".

```js
$("#demo").bind("opened", function(e, section) { //used to be "open"
  console.log(section, " was opened");
});
```

This pull request fixes #38