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/noBlanksBlockQuote.js

@@ -0,0 +1,17 @@
+module.exports = {
+  "name": "MD028",
+  "desc": "Blank line inside blockquote",
+  "tags": [ "blockquote", "whitespace" ],
+  "aliases": [ "no-blanks-blockquote" ],
+  "regexp": null,
+  "func": function MD028(params, errors) {
+    var prevToken = {};
+    params.tokens.forEach(function forToken(token) {
+      if ((token.type === "blockquote_open") &&
+          (prevToken.type === "blockquote_close")) {
+        errors.add(token.lineNumber - 1);
+      }
+      prevToken = token;
+    });
+  }
+};