chore: import upstream snapshot with attribution

tools/challenge-parser/parser/plugins/table-and-strikethrough.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var strikethroughFromMD = require('mdast-util-gfm-strikethrough/from-markdown');
+var tableFromMD = require('mdast-util-gfm-table/from-markdown');
+var strikethrough = require('micromark-extension-gfm-strikethrough');
+var table = require('micromark-extension-gfm-table');
+
+module.exports = tableAndStrikethrough;
+
+function tableAndStrikethrough() {
+  var data = this.data();
+
+  add('micromarkExtensions', strikethrough());
+  add('micromarkExtensions', table);
+  add('fromMarkdownExtensions', strikethroughFromMD);
+  add('fromMarkdownExtensions', tableFromMD);
+
+  function add(field, value) {
+    if (data[field]) data[field].push(value);
+    else data[field] = [value];
+  }
+}
+
+// Based on remark-gfm, extended as described in
+// https://github.com/remarkjs/remark/tree/main/packages/remark-parse#extending-the-parser