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-310-nim-square.md

@@ -1,42 +1,33 @@
 ---
 id: 5900f4a21000cf542c50ffb5
-challengeType: 5
 title: 'Problem 310: Nim Square'
+challengeType: 5
 forumTopicId: 301966
 ---
 
-## Description
-<section id='description'>
+# --description--
+
 Alice and Bob play the game Nim Square.
+
 Nim Square is just like ordinary three-heap normal play Nim, but the players may only remove a square number of stones from a heap.
+
 The number of stones in the three heaps is represented by the ordered triple (a,b,c).
+
 If 0≤a≤b≤c≤29 then the number of losing positions for the next player is 1160.
 
-
 Find the number of losing positions for the next player if 0≤a≤b≤c≤100 000.
-</section>
 
-## Instructions
-<section id='instructions'>
+# --hints--
 
-</section>
-
-## Tests
-<section id='tests'>
-
-```yml
-tests:
-  - text: <code>euler310()</code> should return 2586528661783.
-    testString: assert.strictEqual(euler310(), 2586528661783);
+`euler310()` should return 2586528661783.
 
+```js
+assert.strictEqual(euler310(), 2586528661783);
 ```
 
-</section>
+# --seed--
 
-## Challenge Seed
-<section id='challengeSeed'>
-
-<div id='js-seed'>
+## --seed-contents--
 
 ```js
 function euler310() {
@@ -47,17 +38,8 @@ function euler310() {
 euler310();
 ```
 
-</div>
-
-
-
-</section>
-
-## Solution
-<section id='solution'>
+# --solutions--
 
 ```js
 // solution required
 ```
-
-</section>