Update MD018/no-missing-space-atx to ignore Keycap Number Sign emoji at start of line (fixes #257).

lib/md018.js

@@ -11,7 +11,10 @@ module.exports = {
   "tags": [ "headings", "headers", "atx", "spaces" ],
   "function": function MD018(params, onError) {
     forEachLine(lineMetadata(), (line, lineIndex, inCode) => {
-      if (!inCode && /^#+[^#\s]/.test(line) && !/#\s*$/.test(line)) {
+      if (!inCode &&
+        /^#+[^#\s]/.test(line) &&
+        !/#\s*$/.test(line) &&
+        !line.startsWith("#️⃣")) {
         const hashCount = /^#+/.exec(line)[0].length;
         addErrorContext(
           onError,

test/emoji-headings.md

@@ -0,0 +1,23 @@
+# Emoji Headings
+
+#️⃣ Keycap Number Sign
+
+<https://emojipedia.org/keycap-number-sign/>
+
+# #️⃣ Keycap Number Sign
+
+Text
+
+##️⃣ Keycap Number Sign {MD018}
+
+Text
+
+# Keycap Number Sign #️⃣
+
+Text
+
+# Keycap Number Sign#️⃣
+
+Text
+
+<!-- markdownlint-disable-file MD025 -->