Feat: add new Markdown parser (#39800)

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

curriculum/challenges/english/10-coding-interview-prep/rosetta-code/leap-year.md

@@ -5,51 +5,63 @@ challengeType: 5
 forumTopicId: 302300
 ---
 
-## Description
-
-<section id='description'>
+# --description--
 
 Determine whether a given year is a leap year in the Gregorian calendar.
 
-</section>
+# --hints--
 
-## Instructions
+`isLeapYear` should be a function.
 
-<section id='instructions'>
-
-</section>
-
-## Tests
-
-<section id='tests'>
-
-```yml
-tests:
-  - text: <code>isLeapYear</code> should be a function.
-    testString: assert(typeof isLeapYear == 'function');
-  - text: <code>isLeapYear()</code> should return a boolean.
-    testString: assert(typeof isLeapYear(2018) == 'boolean');
-  - text: <code>isLeapYear(2018)</code> should return <code>false</code>.
-    testString: assert.equal(isLeapYear(2018), false);
-  - text: <code>isLeapYear(2016)</code> should return <code>true</code>.
-    testString: assert.equal(isLeapYear(2016), true);
-  - text: <code>isLeapYear(2000)</code> should return <code>true</code>.
-    testString: assert.equal(isLeapYear(2000), true);
-  - text: <code>isLeapYear(1900)</code> should return <code>false</code>.
-    testString: assert.equal(isLeapYear(1900), false);
-  - text: <code>isLeapYear(1996)</code> should return <code>true</code>.
-    testString: assert.equal(isLeapYear(1996), true);
-  - text: <code>isLeapYear(1800)</code> should return <code>false</code>.
-    testString: assert.equal(isLeapYear(1800), false);
+```js
+assert(typeof isLeapYear == 'function');
 ```
 
-</section>
+`isLeapYear()` should return a boolean.
 
-## Challenge Seed
+```js
+assert(typeof isLeapYear(2018) == 'boolean');
+```
 
-<section id='challengeSeed'>
+`isLeapYear(2018)` should return `false`.
 
-<div id='js-seed'>
+```js
+assert.equal(isLeapYear(2018), false);
+```
+
+`isLeapYear(2016)` should return `true`.
+
+```js
+assert.equal(isLeapYear(2016), true);
+```
+
+`isLeapYear(2000)` should return `true`.
+
+```js
+assert.equal(isLeapYear(2000), true);
+```
+
+`isLeapYear(1900)` should return `false`.
+
+```js
+assert.equal(isLeapYear(1900), false);
+```
+
+`isLeapYear(1996)` should return `true`.
+
+```js
+assert.equal(isLeapYear(1996), true);
+```
+
+`isLeapYear(1800)` should return `false`.
+
+```js
+assert.equal(isLeapYear(1800), false);
+```
+
+# --seed--
+
+## --seed-contents--
 
 ```js
 function isLeapYear(year) {
@@ -57,17 +69,10 @@ function isLeapYear(year) {
 }
 ```
 
-</div>
-</section>
-
-## Solution
-
-<section id='solution'>
+# --solutions--
 
 ```js
 function isLeapYear(year) {
   return year % 100 === 0 ? year % 400 === 0 : year % 4 === 0;
 }
 ```
-
-</section>