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

lib/md043.js

@@ -0,0 +1,44 @@
+// @ts-check
+
+"use strict";
+
+var shared = require("./shared");
+
+module.exports = {
+  "names": [ "MD043", "required-headers" ],
+  "description": "Required header structure",
+  "tags": [ "headers" ],
+  "function": function MD043(params, onError) {
+    var requiredHeaders = params.config.headers;
+    if (requiredHeaders) {
+      var levels = {};
+      [ 1, 2, 3, 4, 5, 6 ].forEach(function forLevel(level) {
+        levels["h" + level] = "######".substr(-level);
+      });
+      var i = 0;
+      var optional = false;
+      var errorCount = 0;
+      shared.forEachHeading(params, function forHeading(heading, content) {
+        if (!errorCount) {
+          var actual = levels[heading.tag] + " " + content;
+          var expected = requiredHeaders[i++] || "[None]";
+          if (expected === "*") {
+            optional = true;
+          } else if (expected.toLowerCase() === actual.toLowerCase()) {
+            optional = false;
+          } else if (optional) {
+            i--;
+          } else {
+            shared.addErrorDetailIf(onError, heading.lineNumber,
+              expected, actual);
+            errorCount++;
+          }
+        }
+      });
+      if ((i < requiredHeaders.length) && !errorCount) {
+        shared.addErrorContext(onError, params.lines.length,
+          requiredHeaders[i]);
+      }
+    }
+  }
+};