Move exec and events components to util module

The exec and events components are common components that
are used by both runtime and registry. It makes sense to
move them into the util package.

This also adds some docs to the registry module

packages/node_modules/@node-red/util/index.js

@@ -17,6 +17,8 @@
 const log = require("./lib/log");
 const i18n = require("./lib/i18n");
 const util = require("./lib/util");
+const events = require("./lib/events");
+const exec = require("./lib/exec");
 
 /**
  * This module provides common utilities for the Node-RED runtime and editor
@@ -54,4 +56,18 @@ module.exports = {
     * @memberof @node-red/util
     */
     util: util,
+
+    /**
+    * Runtime events
+    * @mixes @node-red/util_event
+    * @memberof @node-red/util
+    */
+    events: events,
+
+    /**
+    * Run system commands with event-log integration
+    * @mixes @node-red/util_exec
+    * @memberof @node-red/util
+    */
+    exec: exec
 }