Refactor asset cache Manager + Zend Cache Adaptor

Based on Ocramius review of PR #127, I have taken a stab at refactoring  the Asset Cache Manger to pull services from the SM where possible.  

The provider factory now accepts 4 ways to configure the cache.  Callback, A Zend Service, Class name, and a BC mapper for things like "APC"

Possible way's to configure the caches are as follows:
 
```php
return array(
    'asset_manager' => array(
        'caching' => array(
            //Callback method for BC
            'callback_example.tmp' => array(
                'cache'     => function() {
                    return new myCache();
                },
            ),
            // Zend Service Key
            'zend_service_example.tmp' => array(
                'cache'     => 'myZf2ServiceManagerService',
            ),

            // Classname
            'class_name_example.tmp' => array(
                'cache'     => 'AssetManager\\Cache\\FileManager',
                'options'   => array(
                    'dir' => 'someDir',
                ),
            ),

            // BC Definitions
            'bc_example.tmp' => array(
                'cache'     => 'Apc',
            ),
        ),
    ),
);
```

Also attached is a Zend Cache Adaptor for Assetic.  In order for this to work the adapter needs the cache injected.  As such I have only set this up to be used via the service manager.

To configure this adapter here is one possible solution:

File: MyApplication/Module.php
```php
<?php

namespace Application;

use AssetManager\Cache\ZendCacheAdaptor;
use Zend\Cache\StorageFactory;

class Module
{
    public function getServiceConfig()
    {
        return array(
            'factories' => array(
                'AssetManagerCache' => function ($serviceLocator) {
                    $zfCacheConfig = array(
                        'adapter' => array(
                            'name' => 'Memcached',
                            'options' => array(
                                'servers' => array(
                                    array('localhost','11211'),
                                ),
                                'namespace' => 'zfcache',
                            ),
                        ),
                        'plugins' => array(),
                    );
                    
                    $zendCacheStorage = StorageFactory::factory($zfCacheConfig);
                        
                    return new ZendCacheAdaptor($zendCacheStorage);
                },
            ),
        );
    }
}
```

And my config/autoload/local.php config would look like:
```php
<?php

return array(
    'asset_manager' => array(
        'caching' => array(
            'default' => array(
                'cache'     => 'AssetManagerCache'
            ),
        ),
    ),
);
```