Added output of wp-config options as key value pairs from a hash

Adds an attribute wp_config_options to allow addition of any required configuration in wp-config.php 

A possible solution to #47.

For example

```json
"wordpress": {
  "allow_multisite": true,
  "wp_config_options": {
    "MULTISITE": "true",
    "SUBDOMAIN_INSTALL": "true",
    "DOMAIN_CURRENT_SITE": "'example.com'",
    "PATH_CURRENT_SITE": "'/'",
    "SITE_ID_CURRENT_SITE": "1",
    "BLOG_ID_CURRENT_SITE": "1",
    "SUNRISE": "1",
    "WP_CACHE": "true"
  }
}
```

outputs

```php
/* Multisite */
define( 'WP_ALLOW_MULTISITE', true );

define( 'MULTISITE', true );
define( 'SUBDOMAIN_INSTALL', true );
define( 'DOMAIN_CURRENT_SITE', 'example.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );
define( 'SUNRISE', 1 );
define( 'WP_CACHE', true );
```