Attribute and params support for the iframe embed code

Hey, great class here.
When I was using your class I realized than the iframe embed code cloud not be customized so I modified the code in order to do so.

Now you can do something like:
```php
if ($MediaObject = $this->MediaEmbed->parseUrl('http://www.youtube.com/watch?v=111111')) {
	$MediaObject->setParams(array(
		'autoplay' => 1,
		'loop' => 1
	));
	$MediaObject->setAttributes(array(
		'type' => null,
		'class' => 'iframe-class',
		'data-html5-parameter' => true
	));

	return $MediaObject->getEmbedCode();
}
```
This should return and embed code like:
```html
<embed src="http:/www.youtube.com/embed/111111?autoplay=1&amp;loop=1" class="iframe-class" data-html5-parameter></iframe>
```

**I updated the main classes, tests, examples and README.md files**
I hope you found it usefull.
with returning early no else needed.