Feature/rewrite

hi, 
i added this for make rewrites for caching few things from rewrite rules. I have used for a application and works very well. 

Example for rewrite on varnish: 
https://www.varnish-software.com/static/book/build/exercises/complete-rewrite_urls_and_headers.html?highlight=redirect

Example for my use on puppet: 

```puppet
 varnish::selector { 'cluster1': 
            condition => 'req.request == "GET" && req.url ~ "^/media/images/"',
               rewrite =>  'req.http.host',
        }
```