Move htmllint to npm script.

docs/.htmllintrc

@@ -0,0 +1,18 @@
+{
+  "attr-bans": ["align", "background", "bgcolor", "border", "frameborder", "longdesc", "marginwidth", "marginheight", "scrolling"],
+  "attr-name-style": "dash",
+  "attr-no-unsafe-char": false,
+  "class-style": "dash",
+  "doctype-first": true,
+  "doctype-html5": true,
+  "fig-req-figcaption": true,
+  "html-valid-content-model": false,
+  "id-class-ignore-regex": "(onclick|content|[a-z]+([A-Z][a-z])+)",
+  "id-class-style": "dash",
+  "img-req-alt": false,
+  "indent-style": "spaces",
+  "indent-width": 2,
+  "spec-char-escape": false,
+  "tag-bans": ["b", "i"],
+  "title-max-len": false
+}