Added Microdata class and test

Microdata class allows creating MicrodataParser from different sources.

tests/MicrodataTest.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace YusufKandemir\MicrodataParser\Tests;
+
+use YusufKandemir\MicrodataParser\Microdata;
+use YusufKandemir\MicrodataParser\MicrodataParser;
+
+class MicrodataTest extends \PHPUnit\Framework\TestCase
+{
+    protected $htmlFileName = __DIR__ . '/data/W3C/source.html';
+
+    public function testFromHTML()
+    {
+        $html = file_get_contents($this->htmlFileName);
+        $microdata = Microdata::fromHTML($html);
+
+        $this->assertInstanceOf(MicrodataParser::class, $microdata);
+    }
+
+    public function testFromHTMLFile()
+    {
+        $microdata = Microdata::fromHTMLFile($this->htmlFileName);
+
+        $this->assertInstanceOf(MicrodataParser::class, $microdata);
+    }
+
+    public function testFromDOMDocument()
+    {
+        $dom = new \DOMDocument;
+        $dom->loadHTMLFile($this->htmlFileName);
+
+        $microdata = Microdata::fromDOMDocument($dom);
+
+        $this->assertInstanceOf(MicrodataParser::class, $microdata);
+    }
+}