Implemented header packing logic

tests/Header/HeaderPackerTest.php

@@ -26,5 +26,22 @@ class HeaderPackerTest extends \PHPUnit\Framework\TestCase
 
     }
 
+    public function testPackingExamplesFromRfc7541()
+    {
+        $packer = new HeaderPacker();
 
-}
+        $expect = "\x82\x86\x84\x41\x8c\xf1\xe3\xc2\xe5\xf2\x3a\x6b\xa0\xab\x90\xf4\xff";
+        $in = new HeaderBag([
+            ':method' => 'GET',
+            ':scheme' => 'http',
+            ':path' => '/',
+            ':authority' => 'www.example.com'
+        ]);
+        $out = $packer->packHeaders($in);
+
+        $this->assertEquals($expect, $out);
+
+    }
+
+
+}