Make FnType accept params and content

Signed-off-by: davidarendsen <davidarendsen@hey.com>

src/Type/FnType.php

@@ -4,13 +4,28 @@ namespace Arendsen\FluxQueryBuilder\Type;
 
 class FnType implements TypeInterface
 {
-    public function __construct(string $value)
+    /**
+     * @var mixed $value
+     */
+    protected $value;
+
+    /**
+     * @var string $content
+     */
+    protected $content;
+
+    public function __construct($value, string $content = '')
     {
         $this->value = $value;
+        $this->content = $content;
     }
 
     public function __toString(): string
     {
-        return $this->value;
+        if(is_string($this->value)) {
+            return $this->value;
+        }
+
+        return '(' . implode(', ', $this->value) . ') => ' . $this->content;
     }
 }