Docs: add English language support (#170)

* feat: support lang entry build

* feat: vant support lang switch

* move lang iframe-router to utils & fix router link bug

* add en-US config && add some translation

* chang async. to async_ (support superman cdn)

* add layout translation

* change nav style

* upgrade zan-doc

* fix: doc config

* upgrade zan-doc && remove useless code

* fix changelog generate path

docs/src/utils/iframe-router.js

@@ -0,0 +1,31 @@
+/**
+ * 同步父窗口和 iframe 的 vue-router 状态
+ */
+
+import isMobile from './is-mobile';
+import { setLang } from './lang';
+import { iframeReady } from './iframe';
+
+window.syncPath = function(dir) {
+  const router = window.vueRouter;
+  const isInIframe = window !== window.top;
+  const currentDir = router.history.current.path;
+  const iframe = document.querySelector('iframe');
+
+  if (!isInIframe && !isMobile && iframe) {
+    iframeReady(iframe, () => {
+      iframe.contentWindow.changePath(currentDir);
+    });
+  }
+};
+
+window.changePath = function(path = '') {
+  const pathParts = path.split('/');
+  let lang = pathParts[0];
+  if (path[0] === '/') {
+    lang = pathParts[1];
+  }
+
+  setLang(lang);
+  window.vueRouter.replace(path);
+};