Add Group, Limit, Map, Sort functions

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

tests/Function/SortFunctionTest.php

@@ -0,0 +1,18 @@
+<?php
+declare(strict_types=1);
+
+use Arendsen\FluxQueryBuilder\Function\Sort;
+use PHPUnit\Framework\TestCase;
+
+final class SortFunctionTest extends TestCase {
+
+    public function testSimpleSort()
+    {
+        $expression = new Sort(['foo', 'bar'], true);
+
+        $query = '|> sort(columns: ["foo", "bar"], desc: true) ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+
+}