Signup added. Backend added

node_modules/yallist/iterator.js

@@ -0,0 +1,8 @@
+'use strict'
+module.exports = function (Yallist) {
+  Yallist.prototype[Symbol.iterator] = function* () {
+    for (let walker = this.head; walker; walker = walker.next) {
+      yield walker.value
+    }
+  }
+}