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/noMultipleBlanks.js

@@ -0,0 +1,19 @@
+var shared = require("../shared");
+
+module.exports = {
+  "name": "MD012",
+  "desc": "Multiple consecutive blank lines",
+  "tags": [ "whitespace", "blank_lines" ],
+  "aliases": [ "no-multiple-blanks" ],
+  "regexp": null,
+  "func": function MD012(params, errors) {
+    var maximum = params.options.maximum || 1;
+    var count = 0;
+    shared.forEachLine(params, function forLine(line, lineIndex, inCode) {
+      count = (inCode || line.trim().length) ? 0 : count + 1;
+      if (maximum < count) {
+        errors.addDetailIf(lineIndex + 1, maximum, count);
+      }
+    });
+  }
+};