Move each rule implementation into its own file (fixes #83).

lib/md041.js

@@ -0,0 +1,36 @@
+// @ts-check
+
+"use strict";
+
+var shared = require("./shared");
+
+module.exports = {
+  "names": [ "MD041", "first-line-h1" ],
+  "description": "First line in file should be a top level header",
+  "tags": [ "headers" ],
+  "function": function MD041(params, onError) {
+    var level = params.config.level || 1;
+    var frontMatterTitle = params.config.front_matter_title;
+    var tag = "h" + level;
+    var frontMatterTitleRe =
+      new RegExp(frontMatterTitle || "^\\s*title\\s*[:=]", "i");
+    params.tokens.every(function forToken(token, index) {
+      if (token.type === "heading_open") {
+        if (!((token.lineNumber === 1) || (index > 0)) ||
+            (token.tag !== tag)) {
+          shared.addErrorContext(onError, token.lineNumber, token.line);
+        }
+        return false;
+      } else if (token.type === "html_block") {
+        return true;
+      }
+      if (((frontMatterTitle !== undefined) && !frontMatterTitle) ||
+        !params.frontMatterLines.some(function forLine(line) {
+          return frontMatterTitleRe.test(line);
+        })) {
+        shared.addErrorContext(onError, token.lineNumber, token.line);
+      }
+      return false;
+    });
+  }
+};