Convert backend code to ES modules

Bundling code now with Rollup for its flat bundling and tree shaking
support. Front end code still goes through Webpack for browser support.

lib/common/memoize.js

@@ -22,7 +22,7 @@ function getKey(obj) {
   return k;
 }
 
-function memoize(func) {
+export default function memoize(func) {
   return (...args) => {
     const key = JSON.stringify(args.map(getKey)) + getKey(func);
 
@@ -43,5 +43,3 @@ const interval = setInterval(() => {
 
 // Don't hold Node.js process
 if (interval.unref) interval.unref();
-
-module.exports = memoize;