Move plugins back to root dir

plugins/hello-world/greet.js

@@ -0,0 +1,4 @@
+export function greet() {
+  // Call Rust-provided fn!
+  sayHello('Plugin');
+}

plugins/hello-world/index.js

@@ -0,0 +1,7 @@
+import { greet } from './greet.js';
+
+export function hello() {
+  greet();
+  console.log('Try JSON parse', JSON.parse(`{ "hello": 123 }`).hello);
+  console.log('Try RegExp', '123'.match(/[\d]+/));
+}