Add heading increment rule (#22)

* Add heading increment rule

* Fix test

Author: khiga8

style/accessibility.json

@@ -4,6 +4,7 @@
     "no-duplicate-header": true,
     "no-emphasis-as-header": true,
     "no-generic-link-text": true,
+    "no-heading-increment": true,
     "no-space-in-links": false,
     "ol-prefix": "ordered",
     "single-h1": true,

test/usage.test.js

@@ -17,6 +17,7 @@ describe("usage", () => {
         "no-space-in-links": false,
         "single-h1": true,
         "no-emphasis-as-header": true,
+        "no-heading-increment": true,
         "no-generic-link-text": true,
         "ul-style": true,
         default: true,