Add Group, Limit, Map, Sort functions

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

src/Function/Limit.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Arendsen\FluxQueryBuilder\Function;
+
+class Limit extends Base {
+
+    /**
+     * @var int $limit
+     */
+    private $limit;
+
+    public function __construct(int $limit)
+    {
+        $this->limit = $limit;
+    }
+
+    public function __toString()
+    {
+        return '|> limit(n:' . (string)$this->limit . ') ';
+    }
+
+}