Adds event triggering to callbacks

[rtibbles]

This pull request follows up on #137, to allow events to be listened to, rather than just overwriting default behaviours through setting of callback functions within audiojs.

Also fixes some regex that the closure compiler was incorrectly escaping.

[pangolingo]

Great pull request.

Testing on Internet Explorer 9, this fails. I get an error on the line

event = new Event(eventName);

Seems that syntax isn't supported in this browser. Fixed by changing to

var event = document.createEvent('Event');
event.initEvent(eventName, true, true);

[pangolingo]

Also seeing issues on IE8: it seems custom events are supported, so "onplay" doesn't work. I'm fixing by using jQuery to trigger events:

$(element).trigger(eventName, args);

Unfortunately this creates a jQuery dependency.

[CeloGomesBR]

Hi, good job. I need this! But, how can I use it in a multiple instances? For example, how can I call an external function on play? I want to receive parameters too, like the exact element is playing and your currentTime (if 0 I will do A thing, if not I will do B thing). Thank you,