Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.

curriculum/challenges/english/01-responsive-web-design/basic-html-and-html5/delete-html-elements.md

@@ -6,37 +6,39 @@ videoUrl: 'https://scrimba.com/p/pVMPUv/ckK73C9'
 forumTopicId: 17559
 ---
 
-## Description
-<section id='description'>
+# --description--
+
 Our phone doesn't have much vertical space.
+
 Let's remove the unnecessary elements so we can start building our CatPhotoApp.
-</section>
 
-## Instructions
-<section id='instructions'>
-Delete your <code>h1</code> element so we can simplify our view.
-</section>
+# --instructions--
 
-## Tests
-<section id='tests'>
+Delete your `h1` element so we can simplify our view.
 
-```yml
-tests:
-  - text: Your <code>h1</code> element should be deleted.
-    testString: assert(!code.match(/<h1>/gi) && !code.match(/<\/h1>/gi));
-  - text: Your <code>h2</code> element should be on the page.
-    testString: assert(code.match(/<h2>[\w\W]*<\/h2>/gi));
-  - text: Your <code>p</code> element should be on the page.
-    testString: assert(code.match(/<p>[\w\W]*<\/p>/gi));
+# --hints--
 
+Your `h1` element should be deleted.
+
+```js
+assert(!code.match(/<h1>/gi) && !code.match(/<\/h1>/gi));
 ```
 
-</section>
+Your `h2` element should be on the page.
 
-## Challenge Seed
-<section id='challengeSeed'>
+```js
+assert(code.match(/<h2>[\w\W]*<\/h2>/gi));
+```
 
-<div id='html-seed'>
+Your `p` element should be on the page.
+
+```js
+assert(code.match(/<p>[\w\W]*<\/p>/gi));
+```
+
+# --seed--
+
+## --seed-contents--
 
 ```html
 <h1>Hello World</h1>
@@ -46,18 +48,8 @@ tests:
 <p>Kitty ipsum dolor sit amet, shed everywhere shed everywhere stretching attack your ankles chase the red dot, hairball run catnip eat the grass sniff.</p>
 ```
 
-</div>
-
-
-
-</section>
-
-## Solution
-<section id='solution'>
-
+# --solutions--
 
 ```html
 <h2>CatPhotoApp</h2><p>Kitty ipsum dolor sit amet, shed everywhere shed everywhere stretching attack your ankles chase the red dot, hairball run catnip eat the grass sniff.</p>
 ```
-
-</section>