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

lib/md018.js

@@ -0,0 +1,19 @@
+// @ts-check
+
+"use strict";
+
+var shared = require("./shared");
+
+module.exports = {
+  "names": [ "MD018", "no-missing-space-atx" ],
+  "description": "No space after hash on atx style header",
+  "tags": [ "headers", "atx", "spaces" ],
+  "function": function MD018(params, onError) {
+    shared.forEachLine(params, function forLine(line, lineIndex, inCode) {
+      if (!inCode && /^#+[^#\s]/.test(line) && !/#$/.test(line)) {
+        shared.addErrorContext(onError, lineIndex + 1, line.trim(), null,
+          null, shared.rangeFromRegExp(line, shared.atxHeaderSpaceRe));
+      }
+    });
+  }
+};