Initial ES modules support

lib/stdlib/coroutine.js

@@ -13,8 +13,10 @@
 // Not supported yet: `throw()` on a generator, and `finally` blocks in
 // `return()`, which need exceptions
 
+import { __is_promise, __reject, __resolve } from "jsrt:promise";
+
 // A generator's object is `co` itself
-const __GeneratorProto = {
+export const __GeneratorProto = {
     // The body runs up to its `initial_yield`, after its params
     start() {
         this.step(undefined);
@@ -39,7 +41,7 @@ const __GeneratorProto = {
 // An async fn returns a promise, which its return fulfils. A rejected await
 // rejects it, and the rest of the body does not run, as an uncaught throw at the
 // await would
-const __AsyncProto = {
+export const __AsyncProto = {
     // The body runs up to its first await, in the call
     start() {
         const promise = new Promise(undefined);