use directories for structure

node_modules/ensure-array/ensure-array.js

@@ -0,0 +1,8 @@
+module.exports = function ensureArray(a, b, n) {
+  if (arguments.length === 0) return [];            // no args, ret []
+  if (arguments.length === 1) {                     // single argument
+    if (a === undefined || a === null) return [];   // undefined or null, ret []
+    if (Array.isArray(a)) return a;                 // isArray, return it
+  }
+  return Array.prototype.slice.call(arguments);     // return array with copy of all arguments
+}