Move HTML to Markdown library to Composer

vendor/league/html-to-markdown/src/Converter/ConverterInterface.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace League\HTMLToMarkdown\Converter;
+
+use League\HTMLToMarkdown\ElementInterface;
+
+interface ConverterInterface
+{
+    /**
+     * @param ElementInterface $element
+     *
+     * @return string
+     */
+    public function convert(ElementInterface $element);
+
+    /**
+     * @return string[]
+     */
+    public function getSupportedTags();
+}