First factory implementation

This is a first implementation, waiting for comments and feedbacks

Example of use : 

```php
class CustomStrategy implements Alchemy\Zippy\Strategy\FileStrategy
{
    public function getAdapters()
    {
        return array(CustomAdapter::newInstance());
    }
    public function getFileExtension() 
    { 
        return 'tar.custom';  
    }
}

$factory = Alchemy\Zippy\Factory::load();
// customize GNU Tar inflator
$factory->adapters['gnu-tar.inflator'] = '/usr/local/bin/tar';

$factory->addStrategy(new CustomStrategy());

// returns ZipAdapter
$adapter = $factory->getAdapterFor('zip');
// returns CustomAdapter
$adapter = $factory->getAdapterFor('tar.custom');
```

This PR addresses #10