Add HeaderSlug configurable

Adds HeaderSlug configurable, with the option for the slug function
to be customised.

Co-authored-by: netniV <netniv@hotmail.com>

tests/ParsedownTest.php

@@ -6,6 +6,7 @@ use Erusev\Parsedown\Components\Blocks\Markup as BlockMarkup;
 use Erusev\Parsedown\Components\Inlines\Markup as InlineMarkup;
 use Erusev\Parsedown\Configurables\BlockTypes;
 use Erusev\Parsedown\Configurables\Breaks;
+use Erusev\Parsedown\Configurables\HeaderSlug;
 use Erusev\Parsedown\Configurables\InlineTypes;
 use Erusev\Parsedown\Configurables\SafeMode;
 use Erusev\Parsedown\Configurables\StrictMode;
@@ -59,6 +60,7 @@ class ParsedownTest extends TestCase
             new SafeMode(\substr($test, 0, 3) === 'xss'),
             new StrictMode(\substr($test, 0, 6) === 'strict'),
             new Breaks(\substr($test, 0, 14) === 'breaks_enabled'),
+            new HeaderSlug(\substr($test, 0, 4) === 'slug'),
         ]));
 
         $actualMarkup = $Parsedown->toHtml($markdown);

tests/data/slug_heading.html

@@ -0,0 +1,10 @@
+<h1 id="foo">foo</h1>
+<h1 id="foo-bar">foo bar</h1>
+<h1 id="foobar">foo_bar</h1>
+<h1 id="foobar">foo+bar</h1>
+<h1 id="2rer0ගම්මැද්ද-v-force-ඉනොවේශන්-නේෂන්-සඳහා-එවූ-නි">2rer*(0👍ගම්මැද්ද V FORCE ඉනොවේශන් නේෂන් සඳහා එවූ නි</h1>
+<h2 id="foo">foo</h2>
+<h2 id="foo-bar">foo bar</h2>
+<h2 id="foobar">foo_bar</h2>
+<h2 id="foobar">foo+bar</h2>
+<h2 id="2rer0ගම්මැද්ද-v-force-ඉනොවේශන්-නේෂන්-සඳහා-එවූ-නි">2rer*(0👍ගම්මැද්ද V FORCE ඉනොවේශන් නේෂන් සඳහා එවූ නි</h2>

tests/data/slug_heading.md

@@ -0,0 +1,24 @@
+# foo
+
+# foo bar
+
+# foo_bar
+
+# foo+bar
+
+# 2rer*(0👍ගම්මැද්ද V FORCE ඉනොවේශන් නේෂන් සඳහා එවූ නි
+
+foo
+---
+
+foo bar
+---
+
+foo_bar
+---
+
+foo+bar
+---
+
+2rer*(0👍ගම්මැද්ද V FORCE ඉනොවේශන් නේෂන් සඳහා එවූ නි
+---

tests/src/Configurables/HeaderSlugTest.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Erusev\Parsedown\Tests\Configurables;
+
+use Erusev\Parsedown\Configurables\HeaderSlug;
+use Erusev\Parsedown\State;
+use PHPUnit\Framework\TestCase;
+
+final class HeaderSlugTest extends TestCase
+{
+    /**
+     * @return void
+     * @throws \PHPUnit\Framework\ExpectationFailedException
+     * @throws \SebastianBergmann\RecursionContext\InvalidArgumentException
+     */
+    public function testNamedConstructor()
+    {
+        $State = new State([HeaderSlug::enabled()]);
+
+        $this->assertSame(true, $State->get(HeaderSlug::class)->isEnabled());
+    }
+    /**
+     * @return void
+     * @throws \PHPUnit\Framework\ExpectationFailedException
+     * @throws \SebastianBergmann\RecursionContext\InvalidArgumentException
+     */
+    public function testCustomCallback()
+    {
+        $HeaderSlug = HeaderSlug::withCallback(function (string $t): string {
+            return \preg_replace('/[^A-Za-z0-9]++/', '_', $t);
+        });
+
+        $this->assertSame(
+            'foo_bar',
+            $HeaderSlug->transform('foo bar')
+        );
+    }
+}