Merge pull request buildwithyab#70 from buchin/master

Implement callback within search
```$products = Product::search($term, function($query, $builder){
    return $query->pimp();
})->paginate(12);```

Author: msonowal

src/Engines/MySQLEngine.php

@@ -66,6 +66,10 @@ public function search(Builder $builder)
         $model = $builder->model;
         $query = $model::whereRaw($whereRawString, $params);
 
+        if($builder->callback){
+            $query = call_user_func($builder->callback, $query, $this);
+        }
+
         $result['count'] = $query->count();
 
         if (property_exists($builder, 'orders') && !empty($builder->orders)) {