Moved rules into their own files

Everything under `lib/rules/*` is a rules file (with the name of the rule in camelCase), re-exported into an array in `lib/rules.js`.
Moved the regular expressions from `lib/rules.js` to `lib/expressions.js`, and the rest of the variables into `lib/shared.js`.

lib/rules/noTrailingPunctuation.js

@@ -0,0 +1,21 @@
+var shared = require("../shared");
+var expressions = require("../expressions");
+
+module.exports = {
+  "name": "MD026",
+  "desc": "Trailing punctuation in header",
+  "tags": [ "headers" ],
+  "aliases": [ "no-trailing-punctuation" ],
+  "regexp": expressions.trailingPunctuationRe,
+  "func": function MD026(params, errors) {
+    var punctuation = params.options.punctuation || ".,;:!?";
+    var re = new RegExp("[" + punctuation + "]$");
+    shared.forEachHeading(params, function forHeading(heading, content) {
+      var match = re.exec(content);
+      if (match) {
+        errors.addDetail(heading.lineNumber,
+          "Punctuation: '" + match[0] + "'");
+      }
+    });
+  }
+};