Feat: add new Markdown parser (#39800)

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

curriculum/challenges/english/10-coding-interview-prep/rosetta-code/averages-mode.md

@@ -1,42 +1,48 @@
 ---
-title: Averages/Mode
 id: 594d8d0ab97724821379b1e6
+title: Averages/Mode
 challengeType: 5
 forumTopicId: 302226
 ---
 
-## Description
-<section id='description'>
-Write a program to find the <a href='https://en.wikipedia.org/wiki/Mode (statistics)' title='wp: Mode (statistics)' target='_blank'>mode</a> value of a collection.
+# --description--
+
+Write a program to find the [mode](<https://en.wikipedia.org/wiki/Mode (statistics)> "wp: Mode (statistics)") value of a collection.
+
 The case where the collection is empty may be ignored. Care must be taken to handle the case where the mode is non-unique.
+
 If it is not appropriate or possible to support a general collection, use a vector (array), if possible. If it is not appropriate or possible to support an unspecified value type, use integers.
-</section>
 
-## Instructions
-<section id='instructions'>
+# --hints--
 
-</section>
-
-## Tests
-<section id='tests'>
-
-```yml
-tests:
-  - text: <code>mode</code> should be a function.
-    testString: assert(typeof mode === 'function');
-  - text: <code>mode([1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17])</code> should equal <code>[6]</code>
-    testString: assert.deepEqual(mode(arr1), [6]);
-  - text: <code>mode([1, 2, 4, 4, 1])</code> should equal <code>[1, 4]</code>.
-    testString: assert.deepEqual(mode(arr2).sort(), [1, 4]);
+`mode` should be a function.
 
+```js
+assert(typeof mode === 'function');
 ```
 
-</section>
+`mode([1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17])` should equal `[6]`
 
-## Challenge Seed
-<section id='challengeSeed'>
+```js
+assert.deepEqual(mode(arr1), [6]);
+```
 
-<div id='js-seed'>
+`mode([1, 2, 4, 4, 1])` should equal `[1, 4]`.
+
+```js
+assert.deepEqual(mode(arr2).sort(), [1, 4]);
+```
+
+# --seed--
+
+## --after-user-code--
+
+```js
+const arr1 = [1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17];
+const arr2 = [1, 2, 4, 4, 1];
+```
+
+## --seed-contents--
 
 ```js
 function mode(arr) {
@@ -45,24 +51,7 @@ function mode(arr) {
 }
 ```
 
-</div>
-
-
-### After Test
-<div id='js-teardown'>
-
-```js
-const arr1 = [1, 3, 6, 6, 6, 6, 7, 7, 12, 12, 17];
-const arr2 = [1, 2, 4, 4, 1];
-```
-
-</div>
-
-</section>
-
-## Solution
-<section id='solution'>
-
+# --solutions--
 
 ```js
 function mode(arr) {
@@ -86,7 +75,4 @@ function mode(arr) {
   });
   return result;
 }
-
 ```
-
-</section>