added configuration settings for open/close content/escaped content tags

I was unable to find anyway to be able to read out the `contentTag` and `escapedContentTag` properties of the `BladeCompiler` class. There are no getters, only setters. So here is a solution where I have added extra configuration parameters to allow for custom blade tags

Updated `config.php`
```
<?php return array(

    // Turn on/off minification
    'enabled' => true,
    'blade'   => array(
        'contentTags'        => array('{{', '}}'),
        'escapedContentTags' => array('{{{', '}}}')
    )

);
```

Addresses the following issues:
fitztrev/laravel-html-minify#9 and fitztrev/laravel-html-minify#15