Feat: add new Markdown parser (#39800)

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

curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-280-ant-and-seeds.md

@@ -1,41 +1,29 @@
 ---
 id: 5900f4841000cf542c50ff97
-challengeType: 5
 title: 'Problem 280: Ant and seeds'
+challengeType: 5
 forumTopicId: 301931
 ---
 
-## Description
-<section id='description'>
+# --description--
+
 A laborious ant walks randomly on a 5x5 grid. The walk starts from the central square. At each step, the ant moves to an adjacent square at random, without leaving the grid; thus there are 2, 3 or 4 possible moves at each step depending on the ant's position.
 
 At the start of the walk, a seed is placed on each square of the lower row. When the ant isn't carrying a seed and reaches a square of the lower row containing a seed, it will start to carry the seed. The ant will drop the seed on the first empty square of the upper row it eventually reaches.
 
-What's the expected number of steps until all seeds have been dropped in the top row?
-Give your answer rounded to 6 decimal places.
-</section>
+What's the expected number of steps until all seeds have been dropped in the top row? Give your answer rounded to 6 decimal places.
 
-## Instructions
-<section id='instructions'>
+# --hints--
 
-</section>
-
-## Tests
-<section id='tests'>
-
-```yml
-tests:
-  - text: <code>euler280()</code> should return 430.088247.
-    testString: assert.strictEqual(euler280(), 430.088247);
+`euler280()` should return 430.088247.
 
+```js
+assert.strictEqual(euler280(), 430.088247);
 ```
 
-</section>
+# --seed--
 
-## Challenge Seed
-<section id='challengeSeed'>
-
-<div id='js-seed'>
+## --seed-contents--
 
 ```js
 function euler280() {
@@ -46,17 +34,8 @@ function euler280() {
 euler280();
 ```
 
-</div>
-
-
-
-</section>
-
-## Solution
-<section id='solution'>
+# --solutions--
 
 ```js
 // solution required
 ```
-
-</section>