Add MD036 with tests.

lib/rules.js

@@ -667,5 +667,38 @@ module.exports = [
         }
       });
     }
+  },
+
+  {
+    "name": "MD036",
+    "desc": "Emphasis used instead of a header",
+    "tags": [ "headers", "emphasis" ],
+    "func": function MD036(params, errors) {
+      var lineNumber = 0;
+      function base(token) {
+        lineNumber = token.lineNumber;
+        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")) {
+              errors.push(lineNumber);
+            }
+          };
+        } else if (token.type === "blockquote_open") {
+          return function inBlockquote(t) {
+            if (t.type !== "blockquote_close") {
+              return inBlockquote;
+            }
+          };
+        }
+      }
+      var state = base;
+      params.tokens.forEach(function forToken(token) {
+        state = state(token) || base;
+      });
+    }
   }
 ];