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/noEmphasisAsHeader.js

@@ -0,0 +1,41 @@
+module.exports = {
+  "name": "MD036",
+  "desc": "Emphasis used instead of a header",
+  "tags": [ "headers", "emphasis" ],
+  "aliases": [ "no-emphasis-as-header" ],
+  "regexp": null,
+  "func": function MD036(params, errors) {
+    var punctuation = params.options.punctuation || ".,;:!?";
+    var re = new RegExp("[" + punctuation + "]$");
+    function base(token) {
+      if (token.type === "paragraph_open") {
+        return function inParagraph(t) {
+          if ((t.type === "inline") &&
+              (t.children.length === 3) &&
+              ((t.children[0].type === "strong_open") ||
+                (t.children[0].type === "em_open")) &&
+              (t.children[1].type === "text") &&
+              !re.test(t.children[1].content)) {
+            errors.addContext(t.lineNumber, t.children[1].content);
+          }
+        };
+      } else if (token.type === "blockquote_open") {
+        return function inBlockquote(t) {
+          if (t.type !== "blockquote_close") {
+            return inBlockquote;
+          }
+        };
+      } else if (token.type === "list_item_open") {
+        return function inListItem(t) {
+          if (t.type !== "list_item_close") {
+            return inListItem;
+          }
+        };
+      }
+    }
+    var state = base;
+    params.tokens.forEach(function forToken(token) {
+      state = state(token) || base;
+    });
+  }
+};