[skip CI]smart github CDN with custom script

docs/github-cdn.js

@@ -0,0 +1,30 @@
+const github = (repo) => {
+  const self = {
+    loadScript: (file) => new Promise((resolve, reject) => {
+      const xhr = new XMLHttpRequest();
+      xhr.open('GET', `https://raw.githubusercontent.com/${repo}/master/${file}`);
+      xhr.onload = function () {
+        if (xhr.status === 200) {
+          const u = URL.createObjectURL(new Blob([xhr.responseText], {type: 'text/javascript'}));
+          const s = document.createElement('script');
+          s.src = u;
+          s.onload = resolve;
+          s.onerror = reject;
+          document.body.appendChild(s);
+          document.body.removeChild(s);
+          URL.revokeObjectURL(u);
+        } else
+          reject();
+      };
+      xhr.send();
+    }),
+    loadScripts: (...files) => new Promise((resolve, reject) => {
+      if (!files || !files.length)
+        return resolve();
+      self.loadScript(files.splice(0, 1)).then(() => {
+        self.loadScripts(...files).then(resolve);
+      }).catch(reject);
+    })
+  };
+  return self;
+};